Move third party things to third_party and refactor templates

Summary:
- Combine redundant layout.html into plain_graph.html.
- Break up "hello.html" into separate template files for each ..um.. template.
- Move css into a css file

Test Plan:
./app.py
http://localhost:5000
Try selecting different templates and rendering them

Reviewers: joel, alpert

Reviewed By: joel

Differential Revision: http://phabricator.khanacademy.org/D6158