Move non-Swing-specific object handling upstream

[ctrueden]

See e.g. #72. The logic for whether to use SwingObjectWidget belongs in the abstract layer in scijava-common, so that other UI implementations benefit as well.

[imagejan]

I tried moving the logic from SwingObjectWidget here:

scijava-ui-swing/src/main/java/org/scijava/ui/swing/widget/SwingObjectWidget.java

Lines 99 to 100 in 3c3317f

	return super.supports(model) && ((model.getChoices() != null && model.getChoices().length>0) ||
	((model.getObjectPool() != null) && (model.getObjectPool().size() > 0)));

... into the ObjectWidget interface like this:

	@Override
	public default boolean supports(final WidgetModel model) {
		return InputWidget.super.supports(model) && ((model.getChoices() != null && model.getChoices().length > 0)
				|| ((model.getObjectPool() != null) && (model.getObjectPool().size() > 0)));
	}

... but I cannot call ObjectWidget.super.supports in SwingObjectWidget because there's a more specific override in AbstractInputWidget.

@ctrueden What's the right way to put that logic in the hierarchy of abstract classes and interfaces?