Bug 987237 - Add option to display appIcon in cards; make screenshot preview in cards a settings option

New default/fallback icon for card view

Use span for fallback cards view icon

Move early return to ensure non-screenshot cards still get rotation class

Implement cards view icon as overlay and fallback when screenshot setting is false, or retrieval fails

Fix up getIconURI per bug 988128

Add screenshot cards view setting to developer menu, with initial/default setting value as true

Add tests for enabled and disabled screenshot handling in cards view

Add some getIconURI tests