added Python wrapper for CA code
Added RUNTIME_ASSERT_OR_THROW to enable easier catches of C++ exceptionsfrom ython. Have to investigate if there is a better way of doing it
Changed pure virtual function to the one with empty implementation - this plays easierwith swig interface when we assemble CA simulationin Pthon entirely
Maintenance code changes
Added CACellFieldChangeWatcher.h
Added modules directory with first "plugin" for tracking center of mass of CACell