* rpc: implement websockets with github.com/gorilla/websocket

This change makes package rpc use the github.com/gorilla/websocket
package for WebSockets instead of golang.org/x/net/websocket. The new
library is more robust and supports all WebSocket features including
continuation frames.

There are new tests for two issues with the previously-used library:

  - TestWebsocketClientPing checks handling of Ping frames.
  - TestWebsocketLargeCall checks whether the request size limit is
    applied correctly.

* rpc: raise HTTP/WebSocket request size limit to 5MB

* rpc: remove default origin for client connections

The client used to put the local hostname into the Origin header because
the server wanted an origin to accept the connection, but that's silly:
Origin is for browsers/websites. The nobody would whitelist a particular
hostname.

Now that the server doesn't need Origin anymore, don't bother setting
one for clients. Users who need an origin can use DialWebsocket to
create a client with arbitrary origin if needed.

* vendor: put golang.org/x/net/websocket back

* rpc: don't set Origin header for empty (default) origin

* rpc: add HTTP status code to handshake error

This makes it easier to debug failing connections.

* ethstats: use github.com/gorilla/websocket

* rpc: fix lint

all: update author list and licenses

params: bump hard-coded CHTs to 22nd July values

* Added missing error checks

Add error handling where we assign err a value, but don't check for it being nil.

* core/rawdb: tiny style nit

No need to convert these types.

internal/ethapi: fix debug.chaindbProperty

core: check error before accessing potentially nil block

* signer/core: fix reference issue in key derivation

* Review feedback

* core: fix write coucurrency in txpool

* core: add rlock for pendingState read access

* core: address comments

Gollvm has very aggressive dead code elimination that completely
removes one of these two benchmarks.  To prevent this, use the
result of the benchmark (a boolean), and to be "fair", make the
transformation to both benchmarks.

To be reliably assured of not removing the code, "use" means
assigning to an exported global.  Non-exported globals and
//go:noinline functions are possibly subject to this optimization.

This adds the debug_accountRange method which returns all accounts in
the state for a given block and transaction index.

* eth: fix error when dump config with nil checkpoint

* cmd/utils: ignore default datadir if it's already set.

cmd: encapsulate les relative cli options

cmd, eth, les: fix up ultra light config integration

appveyor: bump builder to Go 1.12.7

core: kill off managed state, use own tiny noncer for txpool

params: bump all CHTs, deploy all checkpoint oracles

* cmd/puppeth: integrate blockscout

* cmd/puppeth: expose debug namespace for blockscout

* cmd/puppeth: fix dbdir

* cmd/puppeth: run explorer in archive mode

* cmd/puppeth: ensure node is synced

* cmd/puppeth: fix explorer docker alignment + drop unneeded exec

* cmd/puppeth: polish up config saving and reloading

* cmd/puppeth: check both web and p2p port for explorer service

Make it select from all live nodes instead of selecting the heads of
random buckets.

* eth: chain config (genesis + fork) ENR entry

* core/forkid, eth: protocol independent fork ID, update to CRC32 spec

* core/forkid, eth: make forkid a struct, next uint64, enr struct, RLP

* core/forkid: change forkhash rlp encoding from int to [4]byte

* eth: fixup eth entry a bit and update it every block

* eth: fix lint

* eth: fix crash in ethclient tests