Pull yourself up by your bootstraps

This is a fairly extensive pull request that completely refactors our view code and adds in the Bootstrap framework.

* Refactors out webflow css code
* Uses bootstrap dynamic column grid, making all screens smooth + mobile responsive
    * makes sidebar collapse on mobile
* Redefines some bootstrap mixins to fit our styles
* Moves custom css (base.css.scss) to SASS
* Makes sidebar steps into links if they've already been completed
* Changes out favicon
* Adds commenting to our view code and CSS to explain what things are doing
* Adds a header with a collapsible Javascript about section
* Adds some '@TODO' comments for areas where we can refactor our code in the future

@maya- that header could use style tweaks
@amymok check out _sidebar code to see how i changed our loop