[Feature] Ability to unmatch an item that has been matched to the wrong game

[Casuallynoted]

At the moment, if a rom is matched to the wrong game but the proper game is not listed on mobygames or igdb, there is no way to specify that it should not carry any metadata from the incorrect match. Having an option to manually unmatch a game would resolve this (and hopefully doing this would prevent it from being rematched during a search).