changes default operation of the class when initialized to DISPOSE_ON_CLOSE. Also renames setupButton() method into initOkButton() for clarity and adds few comments.
adds ability to specify parentFrame to pass to IconDemoApp. So that the window can be positioned neatly above parent frame. Only implemented when constructing IconDemoApp with the SSDialogParams.
adds chaining of the SSDialogParams setters
adds few comments. Also extracts image thumbnail size into constants.
basically decouples ImageFileLoadWorker from IconDemoApp and from ThumbnailAction. Now ImageFileLoadWorker follows SRP and just loads and decodes/processes images.  In order to make ImageFileLoadWorker be able to supply some data back to IconDemoApp I had to introduce IImageEnvelopeReceiver, which is interface for the callback which receives processed images.
adds pde code which will be auto-inserted into sketches to enable them making screenshots on key release.