Updated Item Classification Form

Improvements

The styling on the Classification form has been updated to be consistent with the rest of the site.

Bug fixes

A bug was also fixed in the Classification form that allowed items to have no audience or fiction classification values. Now, there's an empty default value to make it clear that no value is set, only for items that have no initial values. When trying to save empty values, the form will complain and let users know what needs to be updated.