Creating user permission decorator

Signed-off-by: Rodrigo Gonçalves <rodrigosg2000@hotmail.com>
Signed-off-by: Carolina Ramalho <carol15022@hotmail.com>
Modifying style of 404 and 403 pages
Fixing permission required parameter
Merge branch 'user_permission' into devel

Conflicts:
	exam/views.py