JAL-3446 from JAL-3253-applet SequenceFetcher as AsyncSwingWorker

JAL-3446 from JAL-3253-applet SequenceFetcher as AsyncSwingWorker

- uses a javajs.async.SwingJSUtils.StateMachine

- implements a subclass of javajs.async.AsyncSwingWorker, which itself
subclasses SwingWorker

- also required some temporary adjustments for not yet having yet
handled ApplicationSingleton
 on this branch

- added one Preferences final static

- integrates several older methods that together were able to cycle
through a list of items to fetch from a list of possible source
"proxies"

- allows either synchronous (testng) or asynchronous operation simply by
setting the StateMachine's mainLoop timer (0 == synchronous).

- allows JavaScript to display a progress monitor

- allows Java to use a simple Java built in ProgressMonitor for a
SwingWorker-like operation. (easily tested, but not implemented here).

- for more details, see javajs.async.AsyncSwingWorker JavaDoc.