Add some Pure CSS integration

Problem/Motivation

Since YUI Grid is very bland, add some options or perhaps another subtheme based on YUI Grid that utilises some of the components of the new Yahoo Pure CSS project.

Pure CSS uses most of the YUI CSS files and builds on that with some nice defaults for forms, buttons, tables, and menus. This will be useful for sites that don't have a full design set and want common elements to have modern out-of-the-box styles.

http://purecss.io/

Proposed resolution

Add a new sub-theme.

Remaining tasks

• Initial creation of new sub-theme with PureCSS files and some preprocess functions.