Broke backup actions into a subcommand.

Includes edits to command and enum in order to support the subcommand
structure. Removes backup_recovery check from SALVE runs.
Added subcommand tests.

These are tests on src.run.command to ensure that it correctly identifies
and dispatches on subcommands. At present, only backup exists and is tested.
Merge branch 'feature/backup-subcommand' into dev