Make sub-toolbars in pickers possible

Ignore-this: ace153a4684f7b345df56d796717a172
Now all types of buttons kan also be placed in a toolbar picker window. It
should even be possible to create deep nested picker cascades.

darcs-hash:20090528153507-7ad00-828c7a9022b7a4021bf8a74bcd0771373deee254.gz