New camera stuff

[simon-andrews]

New features:

• Added class for Webcam + thread (sorry!)
• Camera feed is now an OpenCV stream with through CSCore's fancy source/sink features
• Added an exposure field on SmartDashboard
• Added a resolution chooser with three built in values

Also, some SmartDashboard keys are now in RobotMap. I thought this would be an interesting change to try out. Not sure if we'll want to stick to this.