Improvements in clump logic - part 3 + 4.

-> part 3: new class clumpTemplate in py/utils.py
   make it possible to create clump templates (python objects)

-> part 4: new method replaceByClumps() in py/wrapper/yadeWrapper.cpp
   replace spheres by clumps using a list of templates and a list of amounts

-> small bug fix in calm() method: now clumps will also be calmed

-> added new example script, that shows usage of clumpTemplate and replaceByClumps()

Thank you all for your help!

https://github.com/yade/trunk/pull/31