* .dockerignore, internal/build: Read git information directly from file

This commit changes the way of retrieving git commit and branch for build
environment from running git command to reading git files directly.

This commit also adds required git files into Docker build context.

fixes: #15346

* .dockerignore: workaround for including some files in .git

* build: enable unconvert linter

 - fixes #15453
 - update code base for failing cases

* cmd/puppeth: replace syscall.Stdin with os.Stdin.Fd() for unconvert linter

Fixes #15373

This changes behaviour: before if the owner/amount didn't match, it
resulted in a successful execution without doing anything; now it
results in a failed execution using the revert opcode (remainder gas
is not consumed).

build: enable gofmt and misspell linters

travis: bump Android NDK version and Android Go builder

* build: [finishes #15372] implements generalized linter and travis job

* .travis, build: minor polishes, disable deadcode

All logs in the FilterLog return value would be the same object 
because the for loop captured the pointer to the iteration variable.

* core: allow price bump at threshold

* core: test changes to allow price bump at threshold

* core: reinstate tx replacement test underneath threshold

* core: minor test failure message cleanups

core, swarm: typo fixes

* les: fix topic ID

* core/bloombits: fix interface conversion

cmd/rlpdump: allow hex input to have leading '0x'

* core, eth, les: fix messy code

* les: fixed tx status test and rlp encoding

* core: add a workaround for light sync

This PR implements the new LES protocol version extensions:

* new and more efficient Merkle proofs reply format (when replying to
  a multiple Merkle proofs request, we just send a single set of trie
  nodes containing all necessary nodes)
* BBT (BloomBitsTrie) works similarly to the existing CHT and contains
  the bloombits search data to speed up log searches
* GetTxStatusMsg returns the inclusion position or the
  pending/queued/unknown state of a transaction referenced by hash
* an optional signature of new block data (number/hash/td) can be
  included in AnnounceMsg to provide an option for "very light
  clients" (mobile/embedded devices) to skip expensive Ethash check
  and accept multiple signatures of somewhat trusted servers (still a
  lot better than trusting a single server completely and retrieving
  everything through RPC). The new client mode is not implemented in
  this PR, just the protocol extension.

* cmd, consensus, core, miner: instatx clique for --dev

* cmd, consensus, clique: support configurable --dev block times

* cmd, core: allow --dev to use persistent storage too

core: fire tx event on replace, expand tests

build: start shipping Ubuntu Artful Aardvark binaries

cmd/faucet: support twitter, google+ and facebook auth too