Configurably attach icons as payload to notification packages. By
design and due to restrictions on mobile devices *only* png is sent.
As KIconLoader preferably returns svg icons from iconPath() we fall
back to loading from "hicolor" using KIconTheme directly. Otherwise
*many* icons are dropped because of svg format.
This also improves slightly the test-case to use a tweaked TestDevice
to allow for inspecting sent NetworkPackage-s.
REVIEW: 126666
