Add ball sensor support

[gerth2]

Add logic in the elevator class to declare and use two sensors to detect the presence of balls in the elevator.

We'll call them the "upper" and "lower" sensors.

If the upper sensor is True, we have one ball in the elevator.

If both sensors are True, we have two balls in the elevator.

Add logic to stop the elevator, intake, and feed wheels when we have two balls in the intake

Add signals to record the values of each sensor.

[gerth2]

https://docs.wpilib.org/en/stable/docs/software/hardware-apis/sensors/digital-inputs-software.html boop

[gerth2]

basic logic added tonight, need to test on robot with gamepieces