OO-2429: move the foreign key from identity to user, remove double mapping of identity, add more unit tests for invitation, unify the methods to create the user and identity

OO-2241: remove optimized getter access to user properties, remove stupid unit test, change unit tests with the !keePEmail option

OO-1483: implement a prewarm infrastructure to warm-up openolat caches, implement it for velocity templates, display names of users and QTI 2.1 resources

OO-887: cache the usernames in UserManager, decouple the AvatarMapper and make it search the username in the cache.

OO-622,CL-225: remove username from GUI in place where is not really needed and students can see it. Mark others place with //TODO username where it need more works and/or the username is only visible by author/coach/admin... Additional fix the setup sql for MySQL (index too long).

--HG--
branch : 80-patch

--HG--
branch : bps