Standardised the meta data downloading system.
Ported Desktop.get_game_info to Vala.
Ported Desktop.get_game_exec to Vala.
Ported Desktop.query_is_game_available to Vala.
Ported Desktop.get_application_black_list to Vala.
Ported Desktop.get_game_reference_for_uri to Vala.
Added MegaDriveROMHeader to Vala, ported MegaDrive.query_is_game_available and MegaDrive.query_is_a_game to Vala.