New: create a custom format without a playgroup

Creating a custom format used to require picking a playgroup you manage first. Now "Create custom format" gives you a "Just me" option too, so you can put together a ruleset on your own — no playgroup needed, and no playgroup required beforehand either. Formats you create this way show up under My Formats on your profile, even before you've tagged any decks or played any matches with them. Whenever you're ready to share one, there's a "Link into a playgroup" button waiting for it there.