Additional style refactoring.
Updates to the LESS files
Complete first full split up of stylesheets
add connect-assets #226

https://github.com/adunkman/connect-assets
use connect-assets to concatenate and minify CSS

This is a similar approach to how I'm dividing up JS files: https://github.com/codeforamerica/streetmix/pull/449
upgrade autoprefixer and configure for connect-assets
remove autoprefixer

https://github.com/codeforamerica/streetmix/pull/458#issuecomment-55812908
Merge branch 'style-refactor'

Conflicts:
	app.js
fix Procfile for Heroku

which was broken by https://github.com/codeforamerica/streetmix/commit/1f735d3d9e1a0cc24e9e9d379e92f849294f4957