OO-449: implements notifications for private message, download of log in course and group, archive of log by course deletion...

OO-449: refactor user session to work with identity key, make it pop, implements one to one chat, group chat, course chat, remove connect user list, refactor UserRequest to make it an interface

OO-449: first part of the implementation: remove smack libraries, refactor controller and unify them, implements messaging across the OpenOLAT event bus, implements administration part to enable chat...