[JRO] Get cucumber features passing

* Classes that are now in the gem need namespacing within `Thredded`
* Features and step defs updated to match the current stack
* Disable minitest during full rake
* Update factories
* Factories need to be created pointing to namespaced classes
* Paths to pages in the thredded gem need to be changed from old to new
* Delete shared view partials that are now in the gem
* Add migration that deletes dupes of user_topic_reads (with matching topic_id and user_id)
[JRO] Update thredded, gemfiles and migrations

* Use latest release of thredded gem
* Copy over migrations and comment out index-related migrations that already exist
* Gems updated (includes cucumber, griddler, etc)