Modified AlbumView to not rely on DOM for storing elements.
AlbumView now uses a map to associate idx->div element, instead of relying on jQuery selectors based on IDs.
Removed unused and unsafe generateId() utility function.
Replaced 'hover' state by a 'selected' class which is programmatically added/removed to thumbnail elements in AlbumView.
Changed semantic of m_children. The indices are not necessarily aligned with the underlying m_item.children(), as elements without photos are skipped.
Removed debug mode log messages.
Added keyboard shortcuts to AlbumView.
Blocked default behavior for keyboard in PhotoView.
Otherwise, hitting 'esc' may navigate outside of the next AlbumView, as well as outside of the PhotoView itself.