When importing a card, its list of subtypes should be set, not just added to

[pbaranay]

Currently, the import function examines a Card's subtypes, gets or creates an appropriate CardSubtype object, and adds a many-to-many linkage for each such CardSubtype. However, we should also take care to delete the many-to-many linkage for any subtypes that have been removed since the last update.

(The same logic applies for supertypes and types.)