[mEIC_det_software] simulation files reorganized to streamline and modularize subsystem and full simulation

[Zhiwen Zhao]

Hi, All

I have simulation files reorganized to streamline and modularize 
subsystem and full simulation
by updating your SVN, you will see the change.

see details at
https://eic.jlab.org/wiki/index.php/EIC_Detector_Software_Simulation#subsystem_simulation

Please let me know any question

Zhiwen