Ticket #145

- implemented group filter (ordered by name) in reporting screen
	- will only appear if groups exist in the selected course
- when a group is selected - only results from enroled students in
the group will be included (eg. no TAs and instructors in the group)
- when a group is selected, the group's name is included in the file name
Refactored navigation bar

Each action now has their own permissions logic. This is so that TAs
can now see the "Run Report" link.