cmd/geth: update flag groups in the geth command usage

common/compiler: add metadata output for solc > 0.4.6

build: bump launchpad builds to Go 1.8.1

Fixes #3608

consensus/ethash: simplify concurrency in VerifyHeaders

Currently http cors and websocket origins are a comma separated string in the
config object. These are replaced with string arrays that are more expressive in
case of a config file.

This change removes a convoluted use of sync/atomic from VerifyHeaders.
It also fixes the annoying error about future blocks.

The genesis block doesn't have a valid ancestor.

cmd/rlpdump: support dumping only the first entity

* p2p/discover, p2p/discv5: add marshaling methods to Node

* p2p/netutil: make Netlist decodable from TOML

* common/math: encode nil HexOrDecimal256 as 0x0

* cmd/geth: add --config file flag

* cmd/geth: add missing license header

* eth: prettify Config again, fix tests

* eth: use gasprice.Config instead of duplicating its fields

* eth/gasprice: hide nil default from dumpconfig output

* cmd/geth: hide genesis block in dumpconfig output

* node: make tests compile

* console: fix tests

* cmd/geth: make TOML keys look exactly like Go struct fields

* p2p: use discovery by default

This makes the zero Config slightly more useful. It also fixes package
node tests because Node detects reuse of the datadir through the
NodeDatabase.

* cmd/geth: make ethstats URL settable through config file

* cmd/faucet: fix configuration

* cmd/geth: dedup attach tests

* eth: add comment for DefaultConfig

* eth: pass downloader.SyncMode in Config

This removes the FastSync, LightSync flags in favour of a more
general SyncMode flag.

* cmd/utils: remove jitvm flags

* cmd/utils: make mutually exclusive flag error prettier

It now reads:

   Fatal: flags --dev, --testnet can't be used at the same time

* p2p: fix typo

* node: add DefaultConfig, use it for geth

* mobile: add missing NoDiscovery option

* cmd/utils: drop MakeNode

This exposed a couple of places that needed to be updated to use
node.DefaultConfig.

* node: fix typo

* eth: make fast sync the default mode

* cmd/utils: remove IPCApiFlag (unused)

* node: remove default IPC path

Set it in the frontends instead.

* cmd/geth: add --syncmode

* cmd/utils: make --ipcdisable and --ipcpath mutually exclusive

* cmd/utils: don't enable WS, HTTP when setting addr

* cmd/utils: fix --identity

cmd/puppeth: format dashboard html, update syncmode flags

* consensus, core, ethstats: use engine specific block beneficiary

* core, eth, les, miner: use explicit beneficiary during mining

* consensus/clique, internal/web3ext: support hash based API queries

* consensus/clique: make RPC return types public

internal/ethapi: Add support for fetching information about the current call in JS traces

- Moved fuse related code in a new package, swarm/fuse
- Added write support
  - Create new files
  - Delete existing files
  - Append to files (with limitations)
- More test coverage

This PR is a prototype implementation of plugable consensus engines and the
Clique PoA protocol ethereum/EIPs#225

eth: announce block after sync cycle (star topology)

* whisper: GetMessages fixed; size restriction updated
* whisper: made PoW and MaxMsgSize customizable
* whisper: test added
* whisper: sym key management changed
* whisper: identity management refactored
* whisper: API refactoring (Post and Filter)
* whisper: big refactoring complete
* whisper: spelling fix
* whisper: variable topic size allowed for a filter
* whisper: final update
* whisper: formatting
* whisper: file exchange introduced in wnode
* whisper: bugfix
* whisper: API updated + new tests
* whisper: statistics updated
* whisper: wnode server updated
* whisper: allowed filtering for variable topic size
* whisper: tests added
* whisper: resolving merge conflicts
* whisper: refactoring (documenting mostly)
* whsiper: tests fixed
* whisper: down cased error messages
* whisper: documenting the API functions
* whisper: logging fixed
* whisper: fixed wnode parameters
* whisper: logs fixed (typos)

travis, appveyor: update to Go 1.8.1