internal/ethapi: add mutex around signing + nonce assignment

This prevents concurrent assignment of identical nonces when automatic
assignment is used.

cmd/puppeth: fix improper key validation for remotes

core: check for gas limit exceeding txs too on new block

consensus/clique: cache block signatures for fast checks

ethstats: don't report transaction content, only hash

cmd, core, eth: configurable txpool parameters

internal/ethapi: fix tx nonces in pool inspect/content

eth: update default gas price when not mining too

eth: don't import propagated blocks during fastsync

Improved Dockerfile?

travis, appveyor: bump to Go 1.8.3, Android NDK 14b

core: fix various golint warnings and errors

1. fix typos
2. methods recevier of struct should be same
3. comments improve

(cherry picked from commit 1ba979539582a00b7fd1a7c8a37a6852e59eac0d)

Rewrite templates for (sub)commands help section

core/vm: allocate stack to 1024

Pre allocate the stack to 1024 optimising stack pushing, reducing calls
to runtime.makeslice and runtime.mallocgc

Enforce 256 bit keys on raw import, support raw mobile imports

consensus, core/*, params: metropolis preparation refactor

cmd/faucet: fix a few typos

Also add the package to the license tool ignore list.

cmd/geth: reintroduce wallet import subcommand