Fallback and MVC dropin changes

Added fallback option (before checkbox and option would simply be hidden
in all browsers) now it is only hidden in browsers that support :checked
(and forced to show in IE7)

Additionally sibling selector for checkbox was changed to ~ since MVC
adds <input type=hidden> after ALL checkboxes

A js file was added to ease drop-in in MVC project since default is not
scaffold checkbox label after checkbox but outside .checkbox div

In essence, you can now drop this into a MVC bootstrap project and it
will work without breaking.