Implements an additional motor ("auxiliary drive") into 2WD kinematic.

This may be used e.g. for tasks like hoisting weights.

• The auxiliary drive is used in operating mode Cyclic Synchronous Velocity and controlled via CANopen-PDOs.
• New PDO mapping is configured with the config-files in folder '/emros/sd-card/2WD_plus_auxiliary'

The merge request correspond to this EMROS-ROS merge request: Link