Elevator subsystem and its respective commands

[pauloalbert]

This pull request adds the code for the Elevator subsystem. The subsystem uses a Talon SRX with Motion Magic control mode to raise the Elevator and a Victor SPX following its outputted current. The subsystem uses four different PIDF gains sets, depending on the elevators state (for the full explanation, see the Javadoc in the subsystem's code).

Commands

• command which moves the elevator to a specific height.
• joystick command to raise and lower the elevator manually.

Subsystem methods

• update method which makes sure the elevator doesn't exceed the allowed heights, and updates the PIDF gains.
• setter for the robot height.
• getter and setter for motor speeds.
• getters for both hall effects states.

[katzuv]

You need to configure the peak target velocity and peak target acceleration for the Elevator. Also, please set the arbitrary feedforward term to zero when the Elevator is all the way down.

@pauloalbert dont forget to set nominal output 1