[Halla12_software] geometry directory moved and solid hit process added

[Zhiwen Zhao]

Hi, folks

I move the geometry directory in svn one level
from
https://clas12svn.jlab.org/repos/trunk/clas12/gemc/production/database_io/halla12/solid 

to
https://clas12svn.jlab.org/repos/trunk/clas12/gemc/production/database_io/solid
This is to match the directory structrue of other experiments.
wiki instruction has been updated accordingly.

Solid hit process is added in svn code, refer to
https://hallaweb.jlab.org/wiki/index.php/Solid_hitprocess#hit_process_list

On wiki, I keep a current svn working version entry which is 4517 now.
I will get all changes if you update to that version.
The version number will be kept up2date. I will remind you for update if 
any made change happens.

I am adding more instruction and reorgnize the wiki page a little bit 
also so that new comer can get invloved more quickly.

cheers

Zhiwen