Fixes #80: Wrapper div should inherit classes from original input elements

Applies to:
 - select (non-multiline)
 - radio
 - checkbox
 - file input

Has the side effect that there is now no way to specify a class to be left on the original select or input element.

A few possible solutions:
 - Leave the class on the element all the time
    - Could result in style conflicts (i.e. styling meant for wrapper div also applies to hidden select/input element.
 - Add an option to either leave the class on or remove it.
 - Take the classes off, but rename them with "uniform-" prefix, similar to how id's are inherited.
 - Use a data attribute such as "data-uniform-class" to specify classes that should be added to the wrapper div
    - Wouldn't work with jQuery < 1.4.3
    - Would require different class definitions for regular inputs that don't use wrapper divs and inputs that do (i.e. class vs. data-uniform-class)