Return a handle h to a new waitbar object.
The waitbar is filled to fraction frac which must be in the range [0, 1].
The optional message msg is centered and displayed above the waitbar.
The appearance of the waitbar figure window can be configured by passing property/value pairs to the function.
When called with a single input the current waitbar, if it exists, is updated to the new value frac. If there are multiple outstanding waitbars they can be updated individually by passing the handle hwbar of the specific waitbar to modify.