[Feature] Email collect message hooks (#331)

- Add email collect hook on creating conversation
- Merge contact if it already exist

db/migrate/20191130164019_add_template_type_to_messages.rb

@@ -0,0 +1,6 @@
+class AddTemplateTypeToMessages < ActiveRecord::Migration[6.0]
+  def change
+    add_column :messages, :content_type, :integer, default: '0'
+    add_column :messages, :content_attributes, :json, default: {}
+  end
+end

db/migrate/20200107164449_add_contact_inbox_to_conversation.rb

@@ -0,0 +1,14 @@
+class AddContactInboxToConversation < ActiveRecord::Migration[6.0]
+  def change
+    add_reference(:conversations, :contact_inbox, foreign_key: true, index: true)
+
+    ::Conversation.all.each do |conversation|
+      contact_inbox = ::ContactInbox.find_by(
+        contact_id: conversation.contact_id,
+        inbox_id: conversation.inbox_id
+      )
+
+      conversation.update!(contact_inbox_id: contact_inbox.id) if contact_inbox
+    end
+  end
+end