Refactor Conversation model (#134)

* 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

config/initializers/event_handlers.rb

@@ -1,2 +1,6 @@
-$dispatcher = Dispatcher.instance
-$dispatcher.load_listeners
+Rails.application.configure do
+  config.to_prepare do
+    Rails.configuration.dispatcher = Dispatcher.instance
+    Rails.configuration.dispatcher.load_listeners
+  end
+end

config/initializers/redis.rb

@@ -1,5 +1,5 @@
 uri = URI.parse(ENV['REDIS_URL'])
-redis = Redis.new(:url => uri)
+redis = Rails.env.test? ? MockRedis.new : Redis.new(:url => uri)
 Nightfury.redis = Redis::Namespace.new("reports", redis: redis)
 
 =begin