Create a cleaner seperation between generating notifications
and updating frontend conversation views. The former is now
handled by `conversation.notify` while the latter is achieved
by triggering an event on the conversation model, which will
only be acted on if there are any views listening for it.
Additionally, instead of re-fetching the entire message history,
which is overkill, just add or update the new/modified message.
This will help speed up the newmessage event handler and also
help avoid unnecessary re-rendering when resolving key conflicts.
// FREEBIE
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