Generate Rails ERB for Legal Docs via Aglio

Instead of having Aglio generate a standalone HTML file, have it generate a ERB partial for rails to render in a view, which gives us headers, footers, and MyUSA styles.

This commit adds:

- myusa.jade -- a Jade template for aglio that generates the ERB
- bootstrap*.jade -- bootstrap helpers for aglio
- a route in home#legal to get to the legal page
- updated rake task
- _aglio.css.scss -- SASS implementation of aglio specific classes

This partially addresses #246 -- still need to move API documentation into rails/ERB.  This only addresses the legal pages.