Run uninstall script async
Otherwise the UI would be blocked. In some cases this is not notable, because we have a dialog open. But especially if we uninstall a package using packagekit the UI is unresponsive for a while.
Maybe we should put the deletion of the files in a separate job or looking towards KF6 at least in a private impl but for now a lambda is the best we can do.
A good way to test this is to install a deb package in the dolphin installer and then click uninstall. With this patch you will still get a hover effect when you move your cursor over the entries while the packagekit authentication dialog is open.