Fixed Solar Panel errors on maps without env_sun, cached sun.

Maps without a env_sun will use 0, 0, 0 which should be fine for most
maps.

Added GM:GetSun - Cached env_sun rather than scrolling through the
entity table every second for each Solar Panel or any other entity that
needs to use the sun in the future.

Randomized the think time on solar panels to 0.8 to 1.2 seconds. Should
resolve a potential case for a lag spike due to all the solar panels
trying to do traces at the same time.