Annotation Tools: Give staff/instructors full permissions (bug fix)

**Note:** In order to facilitate moderation for annotations, staff and instructors need to have write/read/delete/update access to students' annotations. Normally I do it myself, but 4 courses will be starting up that need some self-moderation since I can't do it all on my own.

**Background:** This was supposed to be done by my predecessor but he misunderstood the user attribute ```is_staff``` which is meant for Django admins, not course admins. Having found the way to get roles, I've updated the way that the staff variable is found for all three tools.

**Studio Update:** None.

**LMS Update:** Instructors and Course Staff should have access to students' annotations.

**Testing:** 
1. Load the course using this [tarball](https://www.dropbox.com/s/r684ber7z4ddqtc/2014_T4.DPRfFs.tar.gz).
2. Create three accounts: a student, a course staff, and an instructor.
3. As a student create a text, video, and image annotation.
4. As a course staff and then instructor, try to edit/delete the annotation that the student created.
   a) Before you got the pop-up but no option to edit.
       ![Before permissions](http://i.imgur.com/qVIpw9c.png)
   b) Now you should see the edit/delete options pop up.
       ![After permissions](http://i.imgur.com/MF3pSJx.png)