Adding a QWidget "proxy" on top of QX11EmbedContainer allows reparenting to work correctly - reparenting a QX11EmbedContainer directly kills the client.

This means that the dashboard shows at normal speed again and that the hack for dragging from the desktop to the panel is no longer required.

On another happy note, this commit also happens to make icon transparency work correctly too.
Corruption still creeps in as it always has, but when there's no corruption, things look perfect.