Core fixes

Two core fixes are added: 

- The build system was failing as it expected a SVN repository to get the version of RAT.
-# Removed the references to SVN and HG and only git is used to estimate the version.
-# The RATVERSIONSTR macro was removed and RATVERSION is now expected to be a string extracted from ```git log```. 
-# The build system now creates a ```src/core/Config.hh``` header file, which contains a string holding the RAT version.
- Under certain circumstances (depending how Geant4 was built), RAT would crash due to a duplicated instantiation of ```G4VisManager```. Removed the instantiation from ```rat.cc```, leaving ```GLG4VisManager``` as the sole visualization manager.