Tray icon support for update-manager

It would be good that the update-manager tool could be minimized to a tray icon, with an icon nicely displaying the progress of the update/upgrade. I'm thinking to the way brasero handles this, with a CD icon visually indicating how much has been done.

-The proposed feature make the interaction with the update process much more fluent, and less invasive.
-This would be very useful when doing a distribution update, that can take quite a lot of time.
-This is also helpful for quickly checking the progress of the update and to interact with the process when the user is asked for input.
-The different step of the upgrade (dowloading packaged, installing them, ...) would be indicated with different icons representative of the current process.
-The tray icon will ask the user for attention only when needed, thus limiting the number of pop up windows in the process of the update.
-The tray icon could also have a drop down menu, with options like: restore window, limit bandwidth, pause, cancel, shutdown when finished, and so on. This allows a consistent interaction with the update/uprade process.