Add configuration values for motor driver and/or controller board to config.

[mariolukas]

When the new g-code command is added to the firmware (see https://github.com/mariolukas/FabScanPi-Firmware/issues/6) It would be nice to have the possibility to change the firmware settings like the used board and/or the motor driver scaler by config.

[thatSFguy]

it would be nice if the speed settings were abstracted at the same time into the config (since the are currently hard coded). My MakerBot Digitizer stepper and the DRV8825 had a hard time microstepping at speed=5000, so I just changed them in the python scripts.