started com move operator
gui integration
fix CreateInertialOperator

The operator could create empty objects that would cause problems
when deriving a robot dictionary entry from them even if it was
set in *auto_compute* mode. Now it only creates those objects for
which there is all the information. Anything else has to be created
manually for now.
fix problem with deriving inertial for dictionary

Empty objects would cause an exception here as they would return
None for either props or parent when deriving the dict entry.
no export of material information for obj files

We do want to have the control/information over/on materials in our
models either in URDF or SMURF and not some additional data buried
in the OBJ files themselves or accompanying MTL files.
correct formatting in robotdictionary.py
fix editing of multiple bodies' origins

Editing is at this point only possible in world coordinates, thus only
one side of a robot can be edited. We could include a list of of objects
along with an option to flip sides, but this would clutter the UI a lot.
However, the operator remembers the last numbers punched in, thus it's
easy to repeat the operator on other sides of the robot anyway.
Merge branch 'op_movecom'