Structural changes to the messaging feature.

Messaging is now separated into "Thread" and "Message"
"Thread" contains the list of all participants, the subject, and the list of messages
"Message" contains the body and the sender

Added features:
User is now able to reply directly while viewing messages.
The list of participants is displayed on the top of a thread.
Merge branch 'TEC1-Combined' of https://github.com/myadventure/MyadVenture into TEC1-Combined