Add SimpleKeyTeleop, with simpler keyboard controls

Added is a teleop with simpler controls. Up will make the robot go forward, down backwards, and so on. The robot stops when keys are released.

Some of the code could be modularized from KeyTeleop, but as small modifications had to be made here and there, almost everything had to be touched anyway.

Enabled as a new default.
**TODO**: add runtime controls to change the speed