virtual click targets to enable fancy access to dataset functions

[bgruening]

Now that the new history comes into shape what about adding some virtual drop (as in drag-and-drop) targets.

When you drag a dataset the drop targets are highlighted. One obvious candidate is tool inputs, but we could also display some virtual ones (the circles in the image). One such target could be hide me or visualize me. This could enable quick access to those functions in a fancy way without the need to expand a dataset.

[hexylena]

more radial menus are always good :p