* p2p/discv5: add query delay, fix node address update logic, retry refresh if empty

* p2p/discv5: remove unnecessary ping before topic query

* p2p/discv5: do not filter local address from topicNodes

* p2p/discv5: remove canQuery()

* p2p/discv5: gofmt

* params: update ropsten bootnodes

* params: fix linter

eth, light: minor light client startup cleanups

whisper: improve a log message to analyze a travis issue

This commit reduces database I/O by not writing every state trie to disk.

github: Replaces Wiki link [ci skip]

* les: limit number of LES connections

* eth, cmd/utils: light vs max peer configuration logic

cmd/utils: fix #16006 by not lowering OS ulimit

params: fix bootnodes gofmt

core, eth, les, light: get rid of redundant methods

ethdb: reset the batch size too on reset

* leveldb: Update leveldb to 211f780 (poolfix)

* core, ethdb: reuse database batches

* whisper: message format changed

* whisper: tests fixed

* whisper: style fixes

* whisper: fixed names, fixed failing tests

* whisper: fix merge issue in #15870

Occured while using the github online merge tool. Lesson learned.

* whisper: fix a gofmt error for #15870

* ethapi: add personal.signTransaction

* ethapi: refactor to minimize duplicate code

* ethapi: make nonce,gas,gasPrice obligatory in signTransaction

* whisper: fixes warnings from the code linter

* whisper: more non-API-breaking changes

The remaining lint errors are because of auto-generated
files and one is because an exported function has a non-
exported return type. Changing this would break the API,
and will be part of another commit for easier reversal.

* whisper: un-export NewSentMessage to please the linter

This is an API change, which is why it's in its own commit.
This change was initiated after the linter complained that
the returned type wasn't exported. I chose to un-export
the function instead of exporting the type, because that
type is an implementation detail that I would like to
change in the near future to make the code more
readable and with an increased coverage.

* whisper: update gencodec output after upgrading it to new lint standards

* whisper: fix empty topic

* whisper: add check to matchSingleTopic

* whisper: add tests

* whisper: fix gosimple

* whisper: added lastTopicByte const

* rpc: Support specifying HTTP client in RPC dialing

Adds a minimal interface that captures http.Client and adds a new method
rpc.DialHTTPClient that takes a client using that interface. The existing
rpc.DialHTTP method is then alternatively implemented by using the new
rpc.DialHTTPClient method provided with a standard *http.Client.

* rpc: fix minor doc typos

accounts/abi/bind: support event filtering in abigen

* dashboard: footer, deep state update

* dashboard: resolve asset path

* dashboard: prevent state update on every reconnection

* dashboard: fix linter issue

* dashboard, cmd: minor UI fix, include commit hash

* dashboard: gitCommit renamed to commit

* dashboard: move the geth version to the right, make commit optional

* dashboard: memory, traffic and CPU on footer

* dashboard: fix merge

* dashboard: CPU, diskIO on footer

* dashboard: rename variables, use group declaration

* dashboard: docs

* core, light: fix chain indexer bug

* light: add new CHT

p2p/discv5: logs info about discv5 node info at bind time

* consensus/ethash: add maxEpoch constant

* consensus/ethash: improve cache/dataset handling

There are two fixes in this commit:

Unmap the memory through a finalizer like the libethash wrapper did. The
release logic was incorrect and freed the memory while it was being
used, leading to crashes like in #14495 or #14943.

Track caches and datasets using simplelru instead of reinventing LRU
logic. This should make it easier to see whether it's correct.

* consensus/ethash: restore 'future item' logic in lru

* consensus/ethash: use mmap even in test mode

This makes it possible to shorten the time taken for TestCacheFileEvict.

* consensus/ethash: shuffle func calc*Size comments around

* consensus/ethash: ensure future cache/dataset is in the lru cache

* consensus/ethash: add issue link to the new test

* consensus/ethash: fix vet

* consensus/ethash: fix test

* consensus: tiny issue + nitpick fixes