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.

Update Go and Qt versions in Travis

RPC cleanup

Fix key store address hex decoding and accounts test

Thanks to https://github.com/jaekwon for original fix!

Convert gas values to integers

Implement OS sensitive dataDirs

Allow zero and negative block numbers

topics fix

Fixes #370

* Added an additional tx state which is used to get the current nonce
* Refresh transient state each time a new canonical block is found
* Properly uninstall filters. Fixes a possible crash in RPC

0 is genesis block. Xeth recognises -1 as current

Correct stack size validation for MUL, CALLDATACOPY, EXTCODESIZE, BLOCKH...

Persistent Node Key

* Implemented `eth_logs`
* Fixed issue with `filter.Find()` where logs were appended to an
  incorrect, non-returned slice resulting in no logs found

Don't print per-function testing results