[SAC] "sac" permission group in trac/osgeo

[Sandro Santilli]

FYI:
I've created a "sac" permission group [1] in the osgeo trac instance
and gave it most SPAM privileges (except config).

The group is currently composed by some (not all) the names I found
listed in the "Active members" lits on the SAC wiki page [2].

[1] https://trac.osgeo.org/osgeo/admin/general/perm
[2] https://wiki.osgeo.org/wiki/SAC#Members

--strk;