* Added custom Message-ID and In-Reply-To headers for conversation reply emails
* Added new global config for the default domain (This is used in the above headers)
* Added migration to run the config loader to load the new global config value
* The subject of the conversation reply mailer was made static (This is required for threaded emails)
* Added required tests
* Add Conversation factory with dependent factories
* Include FactoryBot methods in rspec config
* Add unit tests for public methods of Conversation model
* Move Current model into a separate file in lib folder
* Disable Metrics/BlockLength rule for db/migrate and spec folders
* Get rid of global $dispatcher variable
* Create Message#unread_since scope
* Refactor callback methods in Conversation model
* Create Conversations::EventDataPresenter
* Add translation keys for activity messages
* Add pry-rails gem
* Refactor Conversation#notify_status_change
* Add mock_redis for test env
