Added shift+drag of node to panel to create duplicate editor.
Added shift+drag of node to panel to create duplicate editor.

Fixes #575.

GafferHQ/gaffer,andrewkaufman/gaffer,boberfly/gaffer,hradec/gaffer,cedriclaunay/gaffer,paulondc/gaffer,GafferHQ/gaffer,paulondc/gaffer,appleseedhq/gaffer,ivanimanishi/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,davidsminor/gaffer,andrewkaufman/gaffer,ImageEngine/gaffer,lucienfostier/gaffer,chippey/gaffer,davidsminor/gaffer,appleseedhq/gaffer,chippey/gaffer,chippey/gaffer,davidsminor/gaffer,andrewkaufman/gaffer,hradec/gaffer,hradec/gaffer,chippey/gaffer,goddardl/gaffer,GafferHQ/gaffer,goddardl/gaffer,ivanimanishi/gaffer,paulondc/gaffer,lucienfostier/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,boberfly/gaffer,boberfly/gaffer,johnhaddon/gaffer,GafferHQ/gaffer,goddardl/gaffer,ivanimanishi/gaffer,lucienfostier/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,goddardl/gaffer,lucienfostier/gaffer,ImageEngine/gaffer,hradec/gaffer,ivanimanishi/gaffer,ImageEngine/gaffer,GafferHQ/gaffer,davidsminor/gaffer,cedriclaunay/gaffer,cedriclaunay/gaffer,hradec/gaffer,cedriclaunay/gaffer,paulondc/gaffer,boberfly/gaffer,appleseedhq/gaffer,appleseedhq/gaffer