New Fields for Game, new Methods, fixed Iterable error

- added new fields within getGame : publishers, developers, franchises,
date_added (to GiantBomb database), date_last_update(GiantBomb database)

- added new methods : getFranchise, getFranchises

- modified def NewFromJsonDict(data) within Game Class to check whether
the lists parsed (franchises, genres, platforms, images, videos) can be
iterable or not (it gave error before if they were not iterable/didn't
exist). If there are not iterable (at least 1 exists), the fields get
the value None.