Add a deck straight from an event page

Every event's page now also has an Add a deck button, right next to Register match. It opens the deck form with that event's format already selected, so you don't have to hunt for it. For a Limited session it goes a step further: pick Cube Draft and it pre-selects the playgroup's registered cube, or pick Booster Draft or Sealed and it fills in the set name for you. Works the same way for Constructed events too — just with the format pre-picked.