We should either be showing the message tray in the notification or the summary mode.
This is best achieved if the message tray actor contains both, and either one is shown
at any given time.
Queue notifications so that each queued notification is shown when the previous one
times out or when the user is done interacting with the message tray and moves
the mouse away from it. (In the future, we will have some sort of an indication that
there are queued notifications and a way to have the next notification displayed
without moving the mouse away from the message tray.)
Add a message tray that slides out when you move your mouse to
the bottom of the screen. The icons for ongoing conversations
are added to the message tray when the first message in the
conversation is received. The icon is removed when the corresponding
conversation window is closed.
Store the avatar icons in the texture cache and use the checksum for
the data bytes for the icon as the key. This allows to reuse the icon
data for the message tray icon.
Add st_box_layout_insert_actor() that allows inserting an actor at the
arbitrary position in the container. It is needed to be able to add the
icon representing the most recent conversation to the front of the list
of icons in the message tray.
