Naomi Guyer authored Jun 21, 2015 and Robert Lyon committed Jun 26, 2015

* Remove all references to compass.
* Set-up gulp with lib-sass, autoprefixer, and minify. (Easier workflow
to set-up than compass, lib-sass much faster than ruby-sass,
autoprefixer handles browser compatibility for us)
* Add developer documentation on how to work with, or create, themes.

Change-Id: Ia3b3ee829a515865a6cf4407edc64c4943c59557