Support stepper types in the Firmware Updater tool

[hello-binit]

This PR introduces the concept of "stepper types" to the Stretch Factory package. In P5 firmware, @vrathiraj-hellorobot introduced the ability for the uC on a stepper PCB to know which kind of stepper it is (i.e. arm, lift, right wheel, left wheel). In this PR, the firmware updater checks if the stepper already knows its stepper type before erasing the flash memory through a new firmware flash. It saves the stepper_type, flashes the new firmware, then writes the stepper_type to flash memory. This PR also introduces the new tool called REx_stepper_type.py tool for Hello Robot support members to be able to assist Stretch users in flashing their stepper_type bits.

There's a couple benefits to each stepper knowing its stepper_type at the firmware level:

1. The wheels on newer Stretch robots can take advantage of better runstop by actually disconnecting the H bridge from the motor. This makes it easier to backdrive the robot around by tilting the robot and pushing it like a vacuum cleaner.
2. The system check tool can verify that the UDEV rules for each stepper agree with the stepper_type of the stepper. In case the UDEV rules get corrupted, this provides an additional level of redundancy.

[hello-binit]

Please add the stepper type setting/fetching tool into an REx command line tool in this PR. Done