Features/prince

[aedsinger]

This PR includes updates to support the Prince version of Stretch electronics. Notable changes:

• Inclusion of voltage monitoring on the Stepper board
• Move to the BNO085 IMU on the Pimu board
• Inclusion of charge current monitoring on the Pimu
• Measurement of system current using the Efuse instead of shunt on the Pimu
• Move to P4 for Stepper and Pimu

The Wacc board has no relevant changes. The Stepper and Pimu move to hardware_id=3. Currently the IMU is reporting data but there is further work to do:

• Move to IRQ based data read instead of polling (IRQ isn't getting triggered currently)
• Tare / Calibrate the IMU to zero via RPC
• Rotate the reported frame of reference to match that of Stretch RE1/2 (in flash)

For older robots (hardware_id<3 Stepper and Pimu) nothing should change except the move to P4 (which will then include new data fields set to 0)