Changed date format in backup log.

Altered from <year>-<month>-<day>.<epoch> to
<year>-<month>-<day> <hour>:<minute>:<second>
Both are at second-level resolution, but one is more human readable.

Includes addition of commandline backup-recovery argument that raises
an exception that indicates that SALVE does not yet have backup_recovery
support, in case it is invoked with that option before support is added.
Merge branch 'feature/backup-name-by-hash' into dev
Added prompting module for making choices in the console.

Planned use is to select the version of a file to use for recovery.
Cleaned up the prompting module.

Now separates prompting from numerical choices, and adds y/n prompting.
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.

This option is deprecated in favor of the subcommand structure.
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.
Added backup command tests.

Merge branch 'working/feature/backup-recovery' of github.com:sirosen/SALVE into working/feature/backup-recovery

Conflicts:
	src/backup_recovery/prompt.py
	src/run/command.py