Added option to decay to muons

Main changes include:

1. Added an option "--lep" which tells whther JPsi should decay to e-e+ or mu-mu+.

• 0 = e-e+
• 1 = mu-mu+

2. In addition some code cleanup was done

Includes option for t_slope

• The t_slope in previous versions was fixed, and now user can set the t_slope
• In addition in the JPsiGen python code, command line option parser was modified, to eliminate potential bugs

Chage python to python3

As during the test with CVMFS, it didn't work complaining on pyton in shebang line,
A new tag is made for a reference.

Real Photon Flux

The only thing that is different, is real photon flux is added to the total flux.