Fixes #16286

* accounts, eth, clique: implement external backend + move sighash calc to backend

* signer: implement account_Version on external API

* accounts/external: enable ipc, add copyright

* accounts, internal, signer: formatting

* node: go fmt

* flags: disallow --dev in combo with --externalsigner

* accounts: remove clique-specific signing method, replace with more generic

* accounts, consensus: formatting + fix error in tests

* signer/core: remove (test-) import cycle

* clique: remove unused import

* accounts: remove CliqueHash and avoid dependency on package crypto

* consensus/clique: unduplicate header encoding

cmd, core, params: add support for Goerli

New APIs added:

    client.RegisterName(namespace, service) // makes service available to server
    client.Notify(ctx, method, args...)     // sends a notification
    ClientFromContext(ctx)                  // to get a client in handler method

This is essentially a rewrite of the server-side code. JSON-RPC
processing code is now the same on both server and client side. Many
minor issues were fixed in the process and there is a new test suite for
JSON-RPC spec compliance (and non-compliance in some cases).

List of behavior changes:

- Method handlers are now called with a per-request context instead of a
  per-connection context. The context is canceled right after the method
  returns.
- Subscription error channels are always closed when the connection
  ends. There is no need to also wait on the Notifier's Closed channel
  to detect whether the subscription has ended.
- Client now omits "params" instead of sending "params": null when there
  are no arguments to a call. The previous behavior was not compliant
  with the spec. The server still accepts "params": null.
- Floating point numbers are allowed as "id". The spec doesn't allow
  them, but we handle request "id" as json.RawMessage and guarantee that
  the same number will be sent back.
- Logging is improved significantly. There is now a message at DEBUG
  level for each RPC call served.

This change clears up confusion around the two ways in which nodes
can be added to the table.

When a neighbors packet is received as a reply to findnode, the nodes
contained in the reply are added as 'seen' entries if sufficient space
is available.

When a ping is received and the endpoint verification has taken place,
the remote node is added as a 'verified' entry or moved to the front of
the bucket if present. This also updates the node's IP address and port
if they have changed.

* cmd, eth: Added in the flag to step geth once sync based on input

* cmd, eth: 16400 Add an option to stop geth once in sync.

* cmd: 16400 Add an option to stop geth once in sync. WIP

* cmd/geth/main, les/fletcher: added in light mode support

* cmd/geth/main, les/fletcher: Cleaned Comments and code for light mode

* cmd: 16400 Fixed formatting issue and cleaned code

* cmd, eth, les: 16400 Fixed formatting issues

* cmd, eth, les: Performed gofmt to update formatting

* cmd, eth, les: Fixed bugs resulting formatting

* cmd/geth, eth/, les: switched to downloader event

* eth: Fixed styling and gen_config

* eth/: Fix nil error in config file

* cmd/geth: Updated countdown log

* les/fetcher.go: Removed depcreated channel

* eth/downloader.go: Removed deprecated select

* cmd/geth, cmd/utils: Fixed minor issues

* eth: Reverted config files to proper format

* eth: Fixed typo in config file

* cmd/geth, eth/down: Updated code to use header time stamp

* eth/downloader: Changed the time threshold to 10 minutes

* cmd/geth, eth/downloader: Updated downloading event to pass latest header

* cmd/geth: Updated main to use right timer object

* cmd/geth: Removed unused failed event

* cmd/geth: added in correct time field with type assertion

* cmd/geth, cmd/utils: Updated flag to use boolean

* cmd/geth, cmd/utils, eth/downloader: Cleaned up code based on recommendations

* cmd/geth: Removed unneeded import

* cmd/geth, eth/downloader: fixed event field and suggested changes

* cmd/geth, cmd/utils: Updated flag and linting issue

This change resolves multiple issues around handling of endpoint proofs.
The proof is now done separately for each IP and completing the proof
requires a matching ping hash.

Also remove waitping because it's equivalent to sleep. waitping was
slightly more efficient, but that may cause issues with findnode if
packets are reordered and the remote end sees findnode before pong.

Logging of received packets was hitherto done after handling the packet,
which meant that sent replies were logged before the packet that
generated them. This change splits up packet handling into 'preverify'
and 'handle'. The error from 'preverify' is logged, but 'handle' happens
after the message is logged. This fixes the order. Packet logs now
contain the node ID.

dput --passive should make repo pushes from Travis work again.
dput --no-upload-log works around an issue I had while uploading locally.

debuild -d says that debuild shouldn't check for build dependencies when
creating the source package. This option is needed to make builds work
in environments where the installed Go version doesn't match the
declared dependency in the source package.

This PR is replacing the metrics.influxdb.host.tag cmd-line flag with metrics.influxdb.tags - a comma-separated key/value tags, that are passed to the InfluxDB reporter, so that we can index measurements with multiple tags, and not just one host tag.

This will be useful for Swarm, where we want to index measurements not just with the host tag, but also with bzzkey and git commit version (for long-running deployments).

When some of the same messages are redefined anywhere in a Go project,
the protobuf package panics (see
https://github.com/golang/protobuf/issues/178).

Since this package is internal, there is no way to work around it, as
one cannot use it directly, but also cannot define the same messages.

There is no downside in making the package accessible.

Also say that cmd/bootnode is not for production use.

This change unbreaks the build and removes racy access to
disableCheckFreq. Even though the field is set while holding
the lock, it was read outside of the protected section.