fix bug in atom picking code for balls and sticks
fix bug in atom picking code for balls and sticks

The object identifier was not properly set for the tube
and thus it was only possible to pick the atoms themselves
but not the bonds.

This addresses issue #41

yuhangwang/pv,Traksewt/pv,CyrusBiotechnology/pv,CyrusBiotechnology/pv,CyrusBiotechnology/pv,biasmv/pv,biasmv/pv,CyrusBiotechnology/pv,biasmv/pv,biasmv/pv,yuhangwang/pv,Traksewt/pv,yuhangwang/pv,Traksewt/pv,Traksewt/pv,yuhangwang/pv