Enhancement: Deprecate old "selected cards" in favor of JSON First Five support

When I started working on the First Five support on the front-end, I discovered that the old "selected cards" columns for first five, effect costs, and tutor map aren't really appropriate to how I (or other people) use the site. Instead, this should be a JSON column that:

• Has a list at the root. Each element is a dict representing a "First Five":
  • Field for optional name
  • List of slots; each dict has:
    • Field for optional name
    • Field for optional default card stub
    • A list of card stubs (can be arbitrarily long)

The idea here is that the front-end can construct these however the user desires. E.g. if they have a tutored card, they just add a slot with the possible tutor options. If they have multiple First Fives, they can add each alternative. When a First Five is selected, they can highlight which dice will be required, and if they start selecting default cards, it can highlight which cards could not be played given their dice pool.

And the backend just doesn't care about anything other than validating that the card stubs in each list are in the deck and aren't PBs or conjurations, which makes the backend logic extremely simple. And since not even legacy decks on the site currently use the legacy columns, I can just drop them completely without losing backwards compatibility.