Solution for motor_challenge

Dear Ryan,

This is a pull request with a solution for the motor_challenge. 

Inga also asked  me for some feedback:
It is a nice problem to solve. The sample data and organization of the problem is easy to understand. However, I think you  should provide information about robot kinematics  and dynamics. For example, the twist is expressed in the coordinate frame of the robot and wheels are on displaced on robot width in x axes, or data of the motor can be treated as quasistatic.  The challenge would sound more technically correct because now this information has to be inferred from the sample data. Moreover, in sample data twist and motor data seems as linearly dependent measurements, which obviously not the case in the real life.

Best wishes,
 Yury