Renames message column opened -> opened_by_receiver (WIP)
Renames column name "open" in schema.db
Adds sender_id to messages in seed data (hard coding)
Comments out callback method. adding default value in migration
Renames callback method, now assign_conversation_id.
  * removes opened column
Inbox: conversation in bold if unread. (read/unread feature WIP)
Shows inbox messages for logged in customer
Changes opened_by_receiver to true if user goes to convo page
Adds sender_id for message#create