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

Gemfile

@@ -56,10 +56,16 @@ group :development do
   gem 'web-console'
 end
 
+
+group :test do
+  gem 'mock_redis'
+end
+
 group :development, :test do
   gem 'byebug', platform: :mri
   gem 'factory_bot_rails'
   gem 'listen'
+  gem 'pry-rails'
   gem 'rspec-rails', '~> 3.8'
   gem 'rubocop', '~> 0.73.0', require: false
   gem 'seed_dump'