RotationViewer: allow "Move to zero" button to appear independently of the fixed step buttons

Until now, setting showResetToZero to true when constructing a RotationViewer
only caused the "Move to zero" button to appear if fixed step buttons were also
turned on (by calling configureFixedStepButtons).
Add handy command-line program for listing objects in the RMI registry
RotationViewer: allow access to top-level Composite after createControls has been called