Fix bug in asynchronous controller; clean up motion demo.

Asynchronous controller
- Symptom: segfault upon preemption (SendCommandNow()).
- The threading and locking was fine.
- Bug was in removing everything from the queue and adding the first
  element back. Was keeping reference to first element, even though we
  pop it from the queue and invalidate the memory. Now we copy instead;
  fixed bug.

Motion demo
- Removed extraneous code.
- Fixed some (benign) syncing bugs in some of the demos.