Drop content_sao.{cpp,h}

Drop content_sao.{cpp,h}

Move LuaEntitySAO to a new dedicated file
Drop TestSAO (useless object)
Drop the old static startup initialized SAO factory, which was pretty useless.
This factory was using a std::map for 2 elements, now just use a simple condition owned by ServerEnvironment, which will be lightweight, that will also drop a one time useful test on each LuaEntitySAO creation. This should reduce server load on massive SAO creation