Avoid painting -1 values in statistics
Stats optimizations without threshold
Merge branch 'optimize_stats'
Fix teacheradmin urls, add an index one
Add link and copy/paste buttons to nugget's tinyMCEs
Add link and copy/paste buttons to django tinyMCEs too
Use always a '/' at the end of the urls
Some categories can only be assigned by admin
Bugfix, don't lose the admin assigned categories
Show courses' dates in category list