Finish first pass at and docment Bootstrap v2-ish theme

* Adds new "theme" example
* Adds new theme.less file to provide all the overrides and additional
styles for the theme
* theme.less compiles, via Grunt, to two new files to `dist/css`,
bootstrap-theme.css and bootstrap-theme.min.css

less/bootstrap.less

@@ -60,6 +60,3 @@
 // Utility classes
 @import "utilities.less";
 @import "responsive-utilities.less";
-
-// Themes
-@import "theme.less";