Drop legacy commands

This command was meant as a hackish way to upgrade our chain database way back
when nobody cared for live updates and the size of the database along with its
import times was small. With the current database weighing hundreds of GBs and
processing times of many days, this command is just ludicrous.

All the state and block tests are ran as part of our CU builds internally, as
well as have been added to hive black-box tests. As such, there is no reason for
maintaining an extra standalone tool.

Only ethereum/rpc-tests used this command, which hasn't been maintained for over
a year now, a lot of tests failing. What's left of it was moved underneath hive,
which can run the entire test against a black-box geth without special commands.

Also a new RPC test suite is being added which is also based on black box tests,
not needing special commands any more.

Contextual logger

* whisper: wnode updated for tests with geth

* whisper: updated processing of incoming messages

* whisper: symmetric encryption updated

* whisper: filter id type changed to enhance security

* whisper: allow filter without topic for asymmetric encryption

* whisper: POW updated

* whisper: logging updated

* whisper: spellchecker update

* whisper: error handling changed

* whisper: JSON field names fixed

This PR implements a differenceIterator, which allows iterating over trie nodes
that exist in one trie but not in another. This is a prerequisite for most GC
strategies, in order to find obsolete nodes.

Removed exported statedb object accessors, reducing the chance for nasty
bugs to creep in. It's also ugly and unnecessary to have these methods.

travis: only run go vet and misspell on latest Go

travis, appveyor: update builders to Go 1.8

* cmd/geth: added 'geth bug' command

Added bug command to geth, which will open a browser window
with an issue template and some additional system information.

* cmd/geth: update bug with better infos

* cmd/geth: added browser fallback

* cmd/geth: govet yo momma

accounts/usbwallet: swap karalabe/gousb to karalabe/hid

* vendor: add github.com/btcsuite/btcd/btcec

* crypto: add btcec fallback for sign/recover without cgo

This commit adds a non-cgo fallback implementation of secp256k1
operations.

* crypto, core/vm: remove wrappers for sha256, ripemd160

swarm/api/http: fix go vet issue on Go 1.8

vendor: update dependencies with github.com/kardianos/govendor

params: core, core/vm, miner: 64bit gas instructions