Paints a progress bar-style indicator of Engine activity on top of any JComponent using EngineListener.engineActive().
The indicator does not show all the time. It includes logic to predict how much longer the Engine will be active, and shows only when it's going to be busy a while. Once it's shown, it stays visible until the Engine activity declines to zero.
A flag can be set in showWait() to force some static wait text to appear instead of the progress indicator, bypassing the timing logic until the next EngineListener update.