Feature/ibrahim/followed threads

Remove commented out block and pull some stuff into a function to load the first page of results for a thread query.

Conflicts:
	lms/djangoapps/django_comment_client/forum/views.py

Match custom static tabs after discussion URLs so that discussion can actually work.

Feature/victor/static tabs

adding pkg-config

fix ubuntu graphviz lib install

Properly puluralize comments tooltip and change "unread" to "new".

Show total comments instead of unread only, and use a tooltip to show th...

darker background for read posts

Unread counts + tracking for discussion

Change unread to read; makes some things clearer both on the comment service and in the django client

Change unread to read; makes some things clearer both on the comment service and in the django client

- move courseware wiki views above catch-all rule
- handle courses with no custom tabs

* still needs better error checking and testing

Update doc/xml-format.md

Prepare lms for upcoming discussion service changes.

Fixing textbook bugs that didn't appear in 6.002x

This isn't a great fix, but I'm confused what's going on. It's something
in JQuery.TreeView. We write out the HTML correctly, but the lastExpandable
style causes the list item to not be expandable. This didn't bite us in
6.002x because the last item was an appendix that isn't expandable anyway.
It does affect 6.00x, where the last item is Chapter 5 at the moment.

fixed styles for checkboxes

polished multiple choice question styles