Create new incoming and outgoing packages under model.chat.  Also
changed the username field in ChatMessage to receiverUsernames and
make it a list.  In the global chat message, change username to
senderUsername.
Add the other types of outgoing chat messages, which are small
extensions of a new BaseOutgoingChatMessage type.
Add new commands and test classes for the other types of non-global chat
messages.
Change apply to call since it's not sending an array.
Add back in the error handling code and the /queue/errors-suffix logic
on the front-end.
Add the frontend support to make the personal chat process work.