Add a From/To address field in wallet db

[johanneshahn]

The new field From/To Address makes it possible to store the sender/receiver address that was used when creating a new transaction, or receiving a transaction in wallet.
This field is stored outside the slate data and is only available in the wallet db for local usage.

Adds a new optional parameter "addr_to" to api function "tx_lock_outputs".
Adds a new optional parameter "addr_from" to internal function "foreign::receive_tx"

[who-biz]

We spoke about this last week - but for sake of documenting: Holding off on merging/approving this until we can put it behind a show flag like:

epic-wallet txs -show destination

I will start working on this addition.

[who-biz]

ACK

Last commit I made resolved a single merge conflict.

For sake of getting this merged in a timely manner, abandoning idea of putting this behind an optional tag for display. We can handle that later.