Add hints to documentation: GUI not redrawing after migration from GWT RPC

[jschmied]

I got problems with table not redrawing after switching from GWT RPC to Domino REST.

To make migration easy I use a adapter. I had to add scheduleDeferred to it:

	s.get().onSuccess(response -> {
		callback.onSuccess(response);
		Scheduler.get().scheduleDeferred(() -> {
		});
	}).onFailed(errorResponse -> {
		callback.onFailure(buildException(errorResponse));
		Scheduler.get().scheduleDeferred(() -> {
		});
	}).send();

Why Scheduler.scheduleDeferred() is Needed:
GWT applications run in a single-threaded JavaScript event loop. Any UI updates must happen within this event loop to ensure consistent rendering and correct UI behavior.

When you're using:

GWT RPC:
Callbacks are automatically invoked within GWT's event-loop scheduler, which means no manual handling is required.

Domino REST or external JavaScript promises (Elemental2):
Callbacks execute in JavaScript's native promise event queue, outside the GWT event scheduler.
Thus, the GWT framework might not detect that a UI update is needed immediately, resulting in delayed UI redraws.

Using a empty scheduleDeferred flushes the event loop and triggers scheduleFinally() of CellTable. This also prevents flickering.