Add Tan theme and update the demo page
Theme classes now use "theme-" prefix
Fix importing and demo

As it turns out, in LESS 1.3.x, you can't just randomly mix @imports
into the middle of your style rules. Until I have a LESS 1.4-compatible
compiler, we need to keep doing things the way we always have.

Unrelated, the demo was pretty broken, but that's fixed now.
Remove unnecessary nesting in menu.less
Updating branch and fixing merge conflicts
Update structure of the tan theme