hardware

Hardware generation, resolved during initialize from the Device Information Service Model Number (the C core's ba_device_model); until then, and whenever the string is missing or names a different montage than the advertised name, the V2 board of model. Decides which IMU blocks the stream footer carries and how EegChunk.accel is scaled — a HALO V3 has an accelerometer and gyroscope, a HALO V2 has neither.