[packagekit] Notes on UI notifications

[Jud Craft]

Right.  I simply meant that the _result_ notification popups of
PackageKit processes should not time out (by default, in my opinion),
since the user of the computer should always be aware of them.

I don't suppose that PackageKit keeps an internal log of all
transactions, which could be browsed?  This sounds like it would be
very useful for verification and debug purposes.