When renaming files, try to migrate audio files in DB instead of deleting/creating files

[epoupon]

Today, when a file is renamed, the corresponding entry in DB is removed, and a new one is created for the new file.
As a consequence, user stats are lost (stars, listen history).
We could use the track's MBID to identify the track. Checksums seem to be no help here since a rename action may be due to some minor metadata update if the user changed the way to build their file structures.

Note it may not be a big issue when listenbrainz is used to sync listens/loves, as stats are recreated accordingly at the next sync point.