Object selection methods to include objects on attached models

Changed rhinoscriptsyntax methods AllObjects, HiddenObjects, InvertSelectedObjects, ObjectsByName and ObjectsByGroup to include reference objects.

Reason: I ran into troubles using python scripts on a rhino worksession (the group table would contain groups in attached models but ObjectsByGroup would return [] for these groups etc.)

At the moment I cannot see any reason not to include those objects, so I propose merging this into the master.