Automatic activation of loaded data sets in VTK pipeline

If a data set is loaded into the Data Explorer, the respective VtkVisPipelineItem is now automatically selected and activated. I.e. cells can instantly be picked and properties can be changed without selecting the item first.
If more than one item is added at the "same" time (e.g. with geometries), the last item is active (usually the surfaces).

Edit: Also set default highlighting option to false (i.e. bounding boxes are not shown if not explicitly switched on).