OO-2723: store the webfeed in the database instead of xml files to enhance the reliability of blogs and podcasts

OO-2790: add the options to upload assessment documents on a per course element / user base which behave like the user comment

OO-2636: database setup, overview list of participants with statistics and custom attendance rate editor

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

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-2320: log the visit to a binder, ifx an issue where the last modified date of page part are not updated

OO-2057: implement extension of the period where a binder is editable by overriding begin / end dates