MotorVals Message Doesn't Have Thruster Names

[canondetortugas]

Under the new thruster force simulation scheme mentioned here, we need to know which named thruster model corresponds to a given motor value in our motor value message. The MotorVals message currently used by seabee3_driver only contains an array of motor values.

There are two options:

• Modify the ThrusterModel definition from the other issue to include the thruster's index in the MotorVals array.
• Modify the MotorVals message to include a second array with the names of the thruster models that the positions in the motors array correspond to.

The first option would be a little easier to implement and probably have slightly better performance, but the second option is a little more versatile.

[canondetortugas]

Made new MotorPower message which has a power field and a name field. Also made MotorPowerArray.