Add button. Numerous bugfixes

Add button to control the arms.
1) Short press starts or ends tracking.
2) Long press puts the motor in reverse to roll back the arm.

Lots of churn in the code. Hopefully changes from now on will be
incremental and more in tune with the needs of git.

Signed-off-by: Sachin Prabhu <sachin.prabhu@gmail.com>