Gearsbot example uses illogical elevaltor setpoints

[sciencewhiz]

Describe the bug
The GearsBot example uses 5 different elevator setpoints, but there doesn't seem to be much rhyme or reason to them.

On SmartDashboard you can select 0, 0.2, or 0.3
With the gamepad, you can select -0.2 or 0.2
With the PrepareToPickup Command and Pickup Command it uses 0 and 0.25

allwpilib/wpilibjExamples/src/main/java/edu/wpi/first/wpilibj/examples/gearsbot/RobotContainer.java

Lines 50 to 52 in 3d44d8f

	SmartDashboard.putData("Elevator Bottom", new SetElevatorSetpoint(0, m_elevator));
	SmartDashboard.putData("Elevator Platform", new SetElevatorSetpoint(0.2, m_elevator));
	SmartDashboard.putData("Elevator Top", new SetElevatorSetpoint(0.3, m_elevator));

allwpilib/wpilibjExamples/src/main/java/edu/wpi/first/wpilibj/examples/gearsbot/RobotContainer.java

Lines 96 to 97 in 3d44d8f

	dpadUp.whenPressed(new SetElevatorSetpoint(0.2, m_elevator));
	dpadDown.whenPressed(new SetElevatorSetpoint(-0.2, m_elevator));

allwpilib/wpilibjExamples/src/main/java/edu/wpi/first/wpilibj/examples/gearsbot/commands/PrepareToPickup.java

Line 24 in 3d44d8f

parallel(new SetWristSetpoint(0, wrist), new SetElevatorSetpoint(0, elevator)));

allwpilib/wpilibjExamples/src/main/java/edu/wpi/first/wpilibj/examples/gearsbot/commands/Pickup.java

Line 26 in 3d44d8f

parallel(new SetWristSetpoint(-45, wrist), new SetElevatorSetpoint(0.25, elevator)));

Expected behavior
All elevator setpoints should be consistent

Always using 0 and 0.25, across Smartdashboard, gamepad, and commands, and dropping the 0.3 SmartDashboard one. They could also be made into named constants (#1948).