Dataset creation 11048

This tweaks the previous PR https://github.com/openmicroscopy/openmicroscopy/pull/1249 to meet the specs in Gus' gdoc https://docs.google.com/presentation/d/1ygtNV1RxoaGyyQ-ZSJ1x5_3ZLsETNU7otmNWnHcxQeM/

To test:
 - P/D/S creation should be enabled when any tree node is selected (permissions allowing)
    - No difference between toolbar buttons and right-click menu behaviour
 - New P/D/S should become orphans Except Datasets created when Project is selected
 - Currently selected items stay put, Except orphaned Images moved into new Datasets.