new servo methods

[nathan-zeke]

This PR does the following:

• Adds the method writeServoId that writes a new servo ID to any connected servo
• Adds the method listServos that lists any connected servos by attempting to get its position
• Adds usb_path as an initialization parameter to the controller to target a specific USB HID device
• Enhances the getBatteryVoltage method to try for 5 seconds before failing
• Cleans up the _send and _recv methods + some light Python formatting improvements