Merge mobile and desktops styles for #152 and remove obsolete code

This renames "mobile" to "theme-default," loads it via the and moves the associated styles into a media query. In addition, it removes the custom helper class that chose the mobile stylesheet explicitly and the associated footer links. This will give us a base for further refactoring.

In addition, this removes the obsolete "print" stylesheet.

One caveat: by removing the custom helper class and making theme-default media query-specific, it removes the ability to explicitly choose to load an alternate stylesheet.