Implement XEncoder.java

[acarrillo]

Needs to extend SensorHelper, essentially wraps WPIlibj functions but also pushes data to the dashboard.

[acarrillo]

I've renamed the class to avoid conflict and confusion with WPIlibj's Encoder class.

[acarrillo]

I can't fully finish this class without:

• Reaching consensus on the dashboard
  • Should sensors send their data to the dashboard, or should the dashboard poll the sensors?
• Knowing how Config.java is going to work
  • So that encoders can be properly constructed

I'd like to address both at tomorrow's meeting.

[acarrillo]

we've decided not to do this, in light of a better dashboard system. See DashboardUpdater spec in Dashboard planning.