Consistently show hflipped pictures in voting booth

It's more natural for people to line things up with a camera if the
viewfinder shows an hflipped image, which makes the viewfinder act like
a mirror. Preserve a consistent experience by showing the preview and
images hflipped as well.
Issue #927: Grey out voting booth background during photos
Issue #927: Keep camera up during identification step; speed up animations
Fix jank in voting booth wrt viewfinder