Change display of 360 panorama button

Bug: 7300866
-Move pano button to center and make larger
-Pano button visible even when in full-screen mode
-Show edit button only when image editor is available
-Correctly hide bottom controls when switching from
 filmstrip mode to grid mode
Change-Id: I485b1988733bedd0c03e89a261a6ce80be46b9bc