Added a debug flag to the VM which determines if VM output is shown
regardless of the log level set.

* Refund should _always_ go to the origin

Conflicts:
	accounts/account_manager.go

Stub defaultBlock RPC methods

Cleanup DefaultAssetPath

Add automatic locking / unlocking of accounts

Validate block header gas limit

* Add block header gas limit validation in ValidateBlock function,
  see eq 39 and 45 in yellow paper. Before it was calculated _for_
  the block instead of validated.
* Use the block header gas limit when setting the gas pool instead
  of calculating the value for the block.

* Use RWMutex instead of Mutex
* Use time.Duration instead of int for unlock time
* Use time.After with select instead of time.Sleep

* Change account signing API to two sign functions;
  Sign without passphrase - works if account is unlocked
  Sign with passphrase - always works and unlocks the account
* Account stays unlocked for X ms and is then automatically locked

- remove blockpool code
- remove blockpool integration test (kinda embarrassing)
- remove errors.go

- blockpool moves to its own package
- uses errs pkg for its own coded errors
- publicly settable config of params (time intervals and batchsizes)
- test helpers in subpackage
- optional TD in blocks used now to update peers chain info
- major improvement in algorithm
- fix fragility and sync/parallelisation bugs
- implement status for reporting on sync status (peers/hashes/blocks etc)
- several tests added and further corner cases covered

Update Go and Qt versions in Travis

RPC cleanup

Fix key store address hex decoding and accounts test