Backup of overwritten catalogs

[vbonvin]

In order to avoid unfortunate data loss when overwriting .pouet catalogs, it would be good to backup these catalogs in a backup folder.

• [ ] let the user decide of the backup location, either from settings.cfg or directly from the config panel (default must be in the cats directory)
• [ ] add a time signature to each backup
• [ ] keep by default only a limited number of backups (10?) - can be augmented by the user.