Faster transaction inserting: Allow looking up past transactions by Narration field

[pmarciniak]

Currently, fava allows easily looking up previously added Payees with just a few keystrokes, and populating the transaction template based on the last transaction of the chosen Payee. This is awesome and a great help when manually entering transactions.

It would be even more awesome if the same feature was supported in the Narration field.

I often have a few recurring transaction "classes" for each payee. In order to populate the transaction template quickly for the correct transaction class, I ended up adding fake payee suffixes per transaction class. Supporting lookup by Narration field would allow eliminating this hack. Furthermore, it would bring this time-saving feature to people who don't use payees.

[yagebu]

Sounds good. A PR would be welcome.