The transaction pool will now some easily be able to pre determine the
validity of a transaction by checking the following:
* Account existst
* gas limit higher than the instrinsic gas
* enough funds to pay upfront costs
* nonce check
Logs are now recorded per transactions instead of tossing them out after
each transaction. This should also fix an issue with
`eth_getFilterLogs` (#629) Also now implemented are the `transactionHash,
blockHash, transactionIndex, logIndex` on logs. Closes#654.
