OO-2454 Improve performance of video management: replace metadata xml with database adapt track files

OO-2472	: reactivate the user session cache for WebDAV to mitigate DOS like attack, set the session time out for REST and WebDAV session to 5 minutes

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