Fix the names of quality identifiers

720P should be 720p, 1080P should be 1080p. Ref
http://en.wikipedia.org/wiki/720p and http://en.wikipedia.org/wiki/1080p

Note that this update only changes things for new databases. For as
far as I can see the change for existing databases is minimal (only the trainer quality naming and example text). If users really want the P to become a p they need to rebuild their database or change it manually. I think adding migration code for this is a bit extreme... ;)

Fixes #658