remove long-deprecated and completely unused RefCountingDecorator

git-svn-id: https://svn.salilab.org/imp/trunk@17239 e91f8c7b-0e32-4433-a9ac-4502d39a4eab
add support for Undecorators to more nicely cleanup when we remove particles

this addresses issue #229, now need to use it with rigid bodies and hierarchies

git-svn-id: https://svn.salilab.org/imp/trunk@17240 e91f8c7b-0e32-4433-a9ac-4502d39a4eab
fix export symbol

git-svn-id: https://svn.salilab.org/imp/trunk@17241 e91f8c7b-0e32-4433-a9ac-4502d39a4eab