Added Target to vision tracking package.

Target will represent a wrapper for the vision tracking data from the
Dashboard.
Added VisionTrackingCommand to Commands package.

The Command will be used to create TargetCollection(s) that control the
MecanumDrivetrain based on the vision data.
Added TargetCollection to vision package.

TargetCollection will create targets based on the Target wrapper class,
and parse the data string that is received.