Fully implemented getAvailableSlotsAccelerator

 - seems to run without bugs on accelerator and host
 - provides macro overrides
 - provides a polymorphic call, so that the macro also works, if the
   CreationPolicy does not provide the needed function (see
   ModernC++Design p.30)
 - maybe it would be easier/cleaner to define, that each CreationPolicy
   needs to provide the availableSlots functions instead of the typedef