Assign activity webservices draft

Added some of the assign activity webservices.
Renamed the assignment 2.2 related webservices for coherence.
Missing scaffold draft for the submit_assign function
Commented the assign_submit function
Assign activity webservice second draft
Renamed structure classes for Moodle compatibility
Grade Bugfix and added scales support
Fix for the get assignment submission

This commit contains the fix for the get_assignment_submission
web service. The previous implementation raised an exeception
this one outputs an empty submission.
Bugfix in the assign module, check for submissions
Another bugfix in the assign module, check for submissions
Added the Calendar support; draft