Various fixes

- hack around missing applet.id when storing applet geometries (do we
need to reuse the config id? It seems we're fine without)
- improve applet loading: properly parent (we're reparenting twice right
now, but this seems necessary to get the applet rendered.

Applets now kind-of works:
- actions are disabled,
- layering and input seems fine (although some z's are still disabled --
magic?)
- saving geometries and restoring multiple applets works
- resizing and moving behaves as expected

todo:
- fix actions
- Fix backgroundhints,
- verify that we can use translucentbackground
- add busyanimation
- check if immutability works
- try replacing the placeHolder with a shader to see if this is makes it more
fluid
- make placeHolder load on-demand
- simplify AppletAppearance
- configdialog is disabled due to a few crashers: move into config.qml
- ToolBox?