Bibarchive: Looser coupling of archiver

* Finding the latest file has it's own function
Bibarchive: conf + versions_kept

* Config file now stores how many versions of an archive are to be
kept in the FS (NOT mongo).
Bibarchive: Versioning added for FS

* When storing in the FS it only holds a certain number of previous
archives. This number is stored in the config file.
Bibarchive: Cohesion improvement

* get_list_of_record_archvies() returns list of files instead of
split file names