Wallet database refactored so that every query ensures isolation by the network id.
Network id provided when database object is created, thus it is transparent to other parts
of the wallet module.
Additionally every uniqueness index is changed to ensure that it doesn't prevent adding
object with same id but from a different network.
* Store tx and receipt in db and cast it to TransferView on read
* Store Log instead of log index
* Use contract from log and bring back address field
* Add tx status and id fields
[services/wallet] Several changes in API after feedback
- Timestamp from block header stored in blocks table and added to each transfers
- From field is computed from signature to offload this computation from client side
- `history` event is added back, so that client can ignore historical blocks when watching
only for new blocks
- block number and timestamp are marshalled in hex. consistent with ethereum data structures
dmitry