* cmd/utils/flags.go: Applying a String len guard for the gitCommit param of the NewApp()

* cmd/utils: remove redundant clause in if condition

all: switch gas limits from big.Int to uint64

This reverts commits 85a1eda5 (#15792) and c495bca4 (#15787)
because they introduce database writes during tracing.

* eth: uncaptialize tracer preimage error message

* eth: improve very important error message

All inputs are saved into history, including 'invalid' inputs.

This avoids setting CC for the go run invocation, which fails on go1.10.

Fixes #15744

* accounts/abi: handle named ouputs prefixed with underscores

* accounts/abi: handle collinding outputs for struct unpacks

* accounts: handle purely underscore output names

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