[Clas12_software] particles colour in gemc

[Maurizio Ungaro]

Hi,

by request, I'm changing the particle scheme to the colours below. I think the extra infos could be very useful.
Before committing the changes, let me know if you have problems with it or want some changes.

neutrons   black
photons    blue
e-         cyan
protons    orange

pi+        magenta
pi-        yellow

all other particle colours will be based on their charges:

+1  red
  0  white
-1  green

(notice that the charged particle scheme is the opposite of what we have now).

let me know!
mauri