Add options to fully disable metadata recording, and to discard unwanted versions? (v3.4+)

[weirdnumbat]

• Storing metadata seems unnecessary and wasteful, at least to me.
  Currently metadata just contains date/time, but it's a template that will probably be expanded upon.

• In most cases I use 'Regenerate' to discard bad outputs and try again. Different versions might be useful to compare, but there's no point having to store the bad outputs as well.