beginnings of SensorDevice test suite

[Scott Cytacki]

I just added a SensorDevice test suite 

org.concord.sensor.device.SensorDeviceTest 

with two example implementations:

org.concord.sensor.pseudo.PseudoSensorDeviceTest

org.concord.sensor.vernier.labquest.LabQuestSensorDeviceTest

This should make it slightly easier to add new SensorDevice implementations.  For example an Arduino SensorDevice, or an updated Vernier GoIO JNA SensorDevice. 

It doesn't currently cover all of the paths through the SensorDevice interface, but it covers most of the methods. 

If I work more on the sensors I plan to use the SensorDeviceTest class to drive the development, so it should get better over time.  

Eventually it could be seen as something like a Conformance suite to vet new SensorDevice implementations.

Scott