Initial implementation of ENR according to ethereum/EIPs#778

Fixes #15740

accounts/abi refactor

* accounts, consensus, core, eth: make chain maker consensus agnostic

* consensus, core: move CalcDifficulty to Engine interface

* consensus: add docs for calcDifficulty function

* consensus, core: minor comment fixups

* dashboard: minor design change

* dashboard: Flow integration, message API

* dashboard: minor polishes, exclude misspell linter

cmd/puppeth: fix faucet 502 error due to non-exposed HTTP port

New Whisper-level message introduced (PoW requirement),
corresponding logic added, plus some tests.

+ Reworked Method Unpack tests into more readable components
+ Added Method Unpack into slice test

+ adding missing comments
+ small cleanups which won't significantly change
  function body.
+ unify Method receiver name

+ The event slice unpacker doesn't correctly extract element from the
slice. The indexed arguments are not ignored as they should be
(the data offset should not include the indexed arguments).

+ The `Elem()` call in the slice unpack doesn't work.
The Slice related tests fails because of that.

+ the check in the loop are suboptimal and have been extracted
out of the loop.

+ extracted common code from event and method tupleUnpack

Event.tupleUnpack doesn't handle correctly Indexed arguments,
hence it can't unpack an event with indexed arguments.

accounts/abi: include fixed array size in offset for dynamic type

cmd/faucet: fix removal of Twitter zlib compression

* cmd/utils: Add check on hard limit, skip test if below target

* cmd/utils: Cross platform compatible fd limit test

* cmd/utils: Remove syscall.Rlimit in test

* cmd/utils: comment fd utility method

* swarm/api: url scheme bzz-hash to get hashes of swarm content (#15238)

Update URI to support bzz-hash scheme and handle such HTTP requests by
responding with hash of the content as a text/plain response.

* swarm/api: return hash of the content for bzz-hash:// requests

* swarm/api: revert "return hash of the content for bzz-hash:// requests"

Return hashes of the content that would be returned by bzz-raw
request.

* swarm/api/http: handle error in TestBzzGetPath

* swarm/api: remove extra blank line in comment

* cmd, core, eth/tracers: support fancier js tracing

* eth, internal/web3ext: rework trace API, concurrency, chain tracing

* eth/tracers: add three more JavaScript tracers

* eth/tracers, vendor: swap ottovm to duktape for tracing

* core, eth, internal: finalize call tracer and needed extras

* eth, tests: prestate tracer, call test suite, rewinding

* vendor: fix windows builds for tracer js engine

* vendor: temporary duktape fix

* eth/tracers: fix up 4byte and evmdis tracer

* vendor: pull in latest duktape with my upstream fixes

* eth: fix some review comments

* eth: rename rewind to reexec to make it more obvious

* core/vm: terminate tracing using defers

params: add Rinkeby bootnode from Akasha

ethkey is a new tool that serves as a command line interface to
the basic key management functionalities of geth. It currently
supports:
 
 - generating keyfiles
 - inspecting keyfiles (print public and private key)
 - signing messages
 - verifying signed messages

This change inlines the logic of bytesAreProper at its sole
callsite, ABI.Unpack, and applies the multiple-of-32 test only in
the case of unpacking methods. Event data is not required to be a
multiple of 32 bytes long.

Changed the communication protocol for ordinary message,
according to EIP 627. Messages will be send in bundles, i.e.
array of messages will be sent instead of single message.

Fixes #15617

* crypto: ensure that VerifySignature rejects malleable signatures

It already rejected them when using libsecp256k1, make sure the nocgo
version does the same thing.

* crypto: simplify check

* crypto: fix build

Fixes #15672 by creating the datadir when creating the
console. This prevents failing to save the history if no datadir
exists.

* swarm/api: url scheme bzz-list for getting list of files from manifest

Replace query parameter list=true for listing all files contained
in a swarm manifest with a new URL scheme bzz-list.

* swarm: replaace bzzr and bzzi schemes with bzz-raw and bzz-immutable

New URI Shemes are added and old ones are deprecated, but not removed.
Old Schemes bzzr and bzzi are functional for backward compatibility.

* swarm/api: completely remove bzzr and bzzi schemes

Remove old schemes in favour of bzz-raw and
bzz-immutable.

* swarm/api: revert "completely remove bzzr and bzzi schemes"

Keep bzzr and bzzi schemes for backward compatibility. At least
until 0.3 swarm release.

contracts/release: do not print error log if les backend has no peers