added static resources (css/images) and included in builds. resolves #8

Added static resources (CSS and image files). `src/css/app.css` references other CSS and image files. 

No changes to the muilti-file build, though it does now generate an extraneous copy of `reset.css` - not sure if there is an r.js setting to stop that.

Single file build uses `cssIn` as @odoe suggested, but also required `grunt-contrib-copy` to copy background images b/c it appears r.js doesn't trace background image paths through url() the way it does for imported CSS files.

r.js is pretty dang cool.