New format: Vanguard

To do:
- Add a possibility to define an Vanguard Avatar for a deck in the deck editor (the solution should also include a solution to be able to define a commander for the commander format decks). Probably a new deck attribute like deck format is needed to be handled in the deck editor.
- Add a new card type for the Vanguard avatars.
- Implement the handling of the new card type at all neccessary classes (mainly exclude it from unwanted actions).
- Add the new deck and game type for Vanguard (as a commander the avatar has to be added to the command zone and it's abilities have to be active) probably the Vanguard format needs a added new type of selection for the match start because it can be combined with any existing format (maybe without Momir).
- Add image downloading for vanguard images (should also work with Momir format)