Refactor CSS

WIP.

This issue deals with #11, #55, #66, #67, #71, #72, #73, and #78.

I have started a big refactor of all the css for emberui. With this refactor comes new class names that will break existing themes. The was necessary in order to flatten the css rules for a speed boost, and also make theming easier.

Whereas before there was a lot of inheritance in the css, we are doing away with most of it and moving to using mixins to explicitly bring in reusable css. This will make it easier to be inconsistent in some of the styling (for example having different hover effects for different styled buttons) without ripping your hair out.