Missing tax lot functionality

[AArnott]

• Tax lot selection UI in transfer and sell transactions.
  The UnsoldAsset view will need a way to consider assets to be unsold when they were sold by the transaction being examined, so that they are seen as 'available' for selection, since they are in fact already selected.
  When selecting tax lot(s) to close or take from in a transaction, only those assigned to that account and with acquisition dates no newer than the closing date are available for selection.
• What about exchanges (trading BTC for ZEC)?
  We'll need to establish FMV in currency of the trade so that reports can represent a sale of the original tax lot,
  and the new tax lot can report a cost basis in currency.

Reports

• Display unrealized losses and gains, by account.