Use localStorage to check if images previously loaded into browser cache and display them when offline.
Add newly downloaded images into viewable list as they load instead of waiting for all to download first.
If imgur ajax requests fail assume user is offline and display any cached images.
Only download high res images if display area has at least 1 axis with > 1024px.
Let user click notification to dismiss it.
Added higher resolution icon (256x256) for installs.