Permissions refactor

[stefanfoulis]

see previously discarded pull request #130

• no more ugly request object in permission checking methods
• use the standard django object level permissions way of integration (with a custom Authentication Backend)

[stefanfoulis]

to continue the discussion on pull request #130 that was closed because the code got stale:

I had a look at django-guardian and django-permissions. They are both pretty cool projects and django-guardian seems to be very mature and well tested. The problem is, that both of the assume you attach a permissions to a single object. But we inherit permissions for files from the folder they are in. So that model sadly does not work for us.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This will now be closed due to inactivity, but feel free to reopen it.