Bug: No negative speeds in Wheel mode

[NeoChaos12]

It seems that if the motor is set to operate in wheel mode, setting a negative speed results in the motor simply stopping. I checked the specific commands being sent to the motor and it appears that whenever a negative value is published to the /set_speed service, it is internally clipped to 0. Thus, turning the motor counter clockwise in wheel mode is impossible until this bug is resolved.

EDIT: Grammar, typos.