Added accessors for the buttons on VectorDataWidget.
Added accessors for the buttons on VectorDataWidget.

Fixes #1003.

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