[Feature] Email collect message hooks (#331)

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

app/views/api/v1/widget/messages/index.json.jbuilder

@@ -2,6 +2,8 @@ json.array! @messages do |message|
   json.id message.id
   json.content message.content
   json.message_type message.message_type_before_type_cast
+  json.content_type message.content_type
+  json.content_attributes message.content_attributes
   json.created_at message.created_at.to_i
   json.conversation_id message. conversation_id
   json.attachment message.attachment.push_event_data if message.attachment