rename roots -> roots-foundation
remove bootstrap components, install foundation

Foundation uses Bower and SASS/Compass, so the appropriate
config files are added, and the `bower_components` directory
is ignored. Foundation JS and SCSS import paths must point to
`bower_components` though. Grunt tasks are also updated.

Roots' method of concatenating `assets/less/app.less` into
`assets/css/main.min.css` will not quite work using Compass,
AFAIK. CSSMin is brought in to help with this, but it's not ideal.