Feature Request: Sort by fiat value

[C-Otto]

Is your feature request related to a problem? Please describe. Transaction lists are sorted by hash, date, or (absolute) coin value. In addition to this I'd like to sort by (absolute) fiat value.

Describe the solution you'd like It should be possible to use set-transaction-sort-order BY_FIAT_THEN_COINS_THEN... etc.

Additional context See #37