optimize content ratings in app resource (bug 948192)

Rather than having in the app resource:

'content_ratings': {
    'us': <ESRB_RATING>,
    've': <ESRB_RATING>,
    'sp': <PEGI_RATING>,
    'it': <PEGI_RATING>
}

Remove redundancy and refactor to:

'region_rating_bodies': {
    'us': 'esrb',
    've': 'esrb',
    'sp': 'pegi',
    'it': 'pegi',
    ...
},
'content_ratings': {
    'esrb': <ESRB_RATING>,
    'pegi': <PEGI_RATING>,
    'generic': <GENERIC_RATING
}

Greatly reducing the size of the app resource to Fireplace.

Fireplace/Flue being updated.