Tighten up base js

Related to issue #15

+ Grab HTML5shiv from Bower and include in the base JS (must be in
<head>)
+ Remove use of "mustard" css class
+ Simplify mustard/no-mustard. Chop it down to "base" -> "enhanced"
+ Add "base" class to HTML element everywhere
+ Move Modernizr to enhanced library
+ Smaller Modernizr build without the HTML5 shiv