Remember incoming txs

[gabmontes]

All incoming txs have to be stored in the wallet's db right upon being received as "to be processed". Then the txs shall be parsed. If all goes ok, after parsed and the renderer is notified, the txs should be removed from the pending pool.

If, i.e. the wallet receives a tx and while it is parsing the wallet crashes or is closed, there is a chance that the tx is lost. Other scenarios could include new blocks being received while the tx is parsed so the best block marker is advanced and then the tx parsing fails.