Added the ability to override the baseView classNameBindings

This fixes issue #139 by allowing a developer to set _(or disable)_ the `classNameBindings` with a custom wrapper. I know the config key is a little verbose, but I think it makes sense. Added a test and everything looks green.

Anyone trying to use Bootstrap 3 with ember-easyForm will run into this issue when they have a field named "Label" (fairly common).