Bunch of changes that would be useful to be tracked. Updates to third_party dependencies

Summary:
Update Bootstrap CSS to 2.3.1

Fix navbar for new bootstrap version

Update Backbone to 1.0 version

Update underscore to 1.4.4 version

Update bootstrap dropdown plugin to 2.3.1. Same version as css theme

Add exercise summary to main page of dashboards and dropdown menu

Livereload server configuration for dashboards

To use run:
pip install livereload
livereload refresh.py

Image representing exercise summary for dashboards main page

Rather large bunch of external libraries used by exercise summary

Test Plan:
Go to dashboards.khanacademy.org and verify that dropdowns are sitll working

At dashboards.khanacademy.org verify that exercise summary shows up
both in dropdown and main list

Run livereload refresh.py, connect browser plugin and verify that page
is refreshed after every save

Verify that dashboards.khanacademy.org has image under exercise summary.

nothing blows up accidentaly

Reviewers: jace

Reviewed By: jace

Differential Revision: http://phabricator.khanacademy.org/D2228