[JRO] Begin extraction to thredded gem

* Add `thredded` to Gemfile
* Update gems. Add initializer
* Remove routes, add migration, mount engine
* Delete A LOT - Most of this code has been moved to jayroh/thredded_gem.
  Some of this is old cruft and needs removing.
* Update schema
[JRO] Gemfile updates and start renaming tables

The first table to play musical chairs is the messageboards table.
It's been renamed to thredded_messageboards and the "new" engine table has been
renamed, temporarily to "new_thredded_messageboards" so it can stick around
for reference (for now).

* Remove Pseudohelp.
* Remove messageboard and topic helpers from the Application controller
[JRO] Rename tables and delete more files

* Many tables are renamed to their new thredded gem names.
* Many model classes chucked after already being extracted
* Hide topic title/header for now
* Rename the `type` STI column in topics to Thredded::PrivateTopic
[JRO] User registration working & UI updates

* Style updates to get private topics looking normal
* Remove board-specific form elements from the user registration form
* User profile page showing latest topics
* Scrolling changes & miniprofiler tweaks
* Hook into any dom node with the latest read data, not just the body tag
* Rack::MiniProfiler should skip static assets when it profiles. Only look
  at the rails app's paths. Ignored those files w/miniprofiler initializer

TODO: Create a module/mixin to allow someone mounting the engine access to
common data like `thredded_abilities`.
[JRO] Upgrade to Rails 4

LOTS of deleting. GREAT times

* Update secret_token
* Rails 4 adds config.secret_key_base and warns when it doesn't exist.
* Delete more & get sass, compass to work
* Upgrade all gems where needed - mostly compass related libs
* Clean up gitignore
* Delete specs and mailers left over from before extraction
* Upgrade devise for Rails 4
* Replace font-icons with font-icons-rails
  font-icons has a dependency on compass, no rails hooks, and has been
  troublesome so this replaces that with font-icons-rails.
* Viewing and updating user feature specs passing
* Removing messageboard-specific code from registration controller and
  getting to work with strong params
* Oauth-related specs passing
[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)
[JRO] Remove ref to Topic class in old migration

Let that be a lesson to you, kids. Don't use model classes in your
migrations!

Removing reference to `Topic` in the old migration because it doesn't
exist as far as the current state of the app is concerned