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

app/presenters/conversations/event_data_presenter.rb

@@ -0,0 +1,37 @@
+module Conversations
+  class EventDataPresenter < SimpleDelegator
+    def lock_data
+      { id: display_id, locked: locked? }
+    end
+
+    def push_data
+      {
+        id: display_id,
+        inbox_id: inbox_id,
+        messages: push_messages,
+        meta: push_meta,
+        status: status_before_type_cast.to_i,
+        unread_count: unread_incoming_messages.count,
+        **push_timestamps
+      }
+    end
+
+    private
+
+    def push_messages
+      [messages.chat.last&.push_event_data].compact
+    end
+
+    def push_meta
+      { sender: sender.push_event_data, assignee: assignee }
+    end
+
+    def push_timestamps
+      {
+        agent_last_seen_at: agent_last_seen_at.to_i,
+        user_last_seen_at: user_last_seen_at.to_i,
+        timestamp: created_at.to_i
+      }
+    end
+  end
+end