Add SimpleKeyTeleop, with simpler keyboard controls

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 a runtime way to change the speed
Fix quit with 'q'
Remove false statement 'press space to stop'
Merge pull request #1 from po1/simple-teleop

Add SimpleKeyTeleop, with simpler keyboard controls