DiffViewer: View deleted images

DiffViewer: If the image was deleted, load the image from the
 base revision; show file status of the current image with stripes
 down both sides.
themes: Add missing card background for dark theme
Let ZipImageRequest calculate its own URL
Added StripedImageView to support showing the file status with
 an image
PatchSetChangesCard: Enable card when tags are set

Change-Id: I819b9bfb2b52ed1414eda15b63189133d2ba8601