Now, per each account, there is a read-only chat view associated with
it, accessible through its item in the conversations list. This can be
used to place system messages, MOTDs, insignificant errors, etc.
Protocols can send text to this buffer by specifying no "chat_id" in
an IM_MESSAGE_RECEIVED message.
The ConversationListView is now an BOutlineListView, and rooms are
added as subitems to the item of their associated account. Right now,
account items aren't selectable or useful.