Improved API data

This pull request adds more information in the REST API:

- Account transactions now have a "receiveddate" and "confirmationdate" field.
- Transaction recipients now have additional "label" and "islocal" field. The islocal field is True if the recipient belongs to your account. 
- Addresses now have an addition "balance" and "relatedtxs" field. The relatedtxs field is a list of all transaction hashes that have either sent money to the address or spent money from that address.