Enabling heatbed associated with materials in the cloud

[pschuster]

If heatbed is activated it should heat up along the nozzle. Printing should start once both the nozzle and the heatbed have reached desired temperature.

There might be printers that have no heatbed installed. In this case we must either sense if there is a heatbed available and exclude that in the preheat phase or we must make sure that fireware does not wait for the heatbed to reach temperature when we only receive 0 degrees value back from printer status.