Removed ObjectSourceBase todo.
Removed ObjectSourceBase todo.

As we slowly leave Cortex procedurals behind, there seems to be less and less of a case for IECore::Group anyway. The Grid node provides a good example for anyone wishing to create a hierarchy source.

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