[JRO] Fix breaking topics#edit form

`category_options` was being called on a Topic object, and the method
doesn't exist. But decorating the topic, and adding the method to the
decorator fixes it.

Also add correct, and uniform, css classes to the div wrapping around
the topic edit form.
[JRO] Format code and fix ordering issue in spec

* Some fixes to the formatting in this file while I'm in here (thx
  rubocop!)
* A spec down below was setting the cofniguration on the Thredded
  singleton and wasn't cleaning up after itself. Therefore, depending on
  the order of the tests being run, it would bleed over into subsequent
  tests and cause failure. This commit resets `Thredded.user_path` after
  it is changed