store info file contents in database
the info file contains information needed to recover swap funds in case of a swapd crash (after funds are locked but before they are claimed). currently, it's just stored in a json file that's written to disk. however, this info can be stored in the database instead now that we have one, and cleared out upon swap completion.

this will also allow for `swapcli` functionality to be built that allows users to easily query for completed vs. ongoing swaps.