Bug fixes

The notifications have finally been fixed. They're not as annoying anymore
and will only show one message at a time and won't display itself
everytime you refresh the (or a) page.

I've added navigation links in the header for course related things so you
can easily navigate back without having to click on catalog first etc.

I've also redirected the documents, files and schedules to their own pages
when you've done any action.

See the commit changes for more details.