Added Durk's first stab at clouds.

Added Durk's first stab at clouds.
Added Simulator/Clouds/
Durk fixed a problem in gui.cxx with cursor type.
Durk updated his time zone / time-offset command line parameters
Curt added a cheezy fade in/out as we transition through the cloud layer.
  We really need to fog the sky dome, sun, moon, stars as well.
Curt added --enable/disable-clouds and --clouds-asl= to control clouds.