Convert Arm class to interface

[AceiusRedshift]

Michael recently began to encounter errors on the test bot relating to the arm, since it does not have one. In order to resolve this issue, I have devised the following fix:

1. Create an interface around the Arm class (ArmInterface)
2. Rename the Arm class to RealArm and make it extend from the interface
3. Create a dummy subsystem DummyArm that implements the interface but does not actually execute any code
4. When setting the value of RobotContainer.arm, use a ternary operator to detect if the robot has an arm (using the bot-dependant constant ArmConstants.HAS_ARM) and decide what class to instantiate.

[MeowAzalea]

LGTM 👍 thumbs up! Lets get that bread team! YIPPEE. 8032 REDSHIFT #1 YEAAHHH!!!!!!!