frontend redesign (bootstrap v3, responsive, less)

Frontend redesign of nearly all the hyperkitty pages. The changes in this PR mostly stem from: 
1) porting site from bootstrap v2 to v3, 
2) maximizing use of bootstrap css/components, 
3) leveraging bootstrap to make site fully responsive at various viewports (from 320px and up), 
4) using LESS instead of CSS (to allow access to/use of certain bootstrap variables)

Fixed pages include the list overview page (example below at 1024px viewport and 480px viewport):
![listoverview-nopersonal 1024px](https://f.cloud.github.com/assets/1501884/2406631/03bdb156-aa75-11e3-828a-e8fe7339021c.png)
![listoverview-personal 480px](https://f.cloud.github.com/assets/1501884/2406641/4724e8ce-aa75-11e3-97c1-ebe1bd3c543e.png)

Other fixed pages include the list of lists page, the list of threads page, the view discussion page, the search result page, the user profile page, and the login page. 

Navbar has changed: explicit breadcrumbs have been removed, but backtracking links are implicit on any given page. Navbar also contains links to features (categories, tags, and users) that haven't been implemented yet (they have been stubbed out with a 404 page containing a custom message). [Content for these features will be in a different PR and will require the USE_MOCKUP flag to work]