Revert "added NTracks for WC to tree. Needed to calc efficiency."

This reverts commit 827d3a5975f5efd57eea50883191f4c7d9be033c.
created file for pi0-example main.
created file for eta-example main.
moved Init functions to GConfigFile. No overloaded function needed in Physics class.
error checking in GTreeParticle::Particle, to avoid seg fault.