cf-tab proposal update

I took @danny8000's thoughtful work and formatted it to be more Capital Frameworky.

Here's a little breakdown of what I did:
- Ditched the research files to keep the repo clean. We can refer back to your repo @danny8000 to keep that history if you want.
- Made sure that the build process was similar to other CF components.
- Updated the naming conventions in the Less file to use our version of BEM. If you're interested you can read more about it on the cf docs site here: http://cfpb.github.io/capital-framework/contributing/#follow-our-css-naming-conventions
- Cleaned up the JS to more closely follow idiomatic.js. (Just realizing that we don't mention that in the docs site, I should rectify that.)
- Safari doesn't allow you to tab to links or buttons without changing your settings. But if you are using VoiceOver it will allow you to tab to buttons by default, so I switched from links to buttons. For verification see [stackoverflow](http://stackoverflow.com/questions/1848390/safari-ignoring-tabindex) and the [apple forums](https://discussions.apple.com/thread/1271082?tstart=0).
- Minor refactoring and style tweaks.