some work on replacing embedded gifs
Revert "some work on replacing embedded gifs"

This reverts commit ac08477096463ce2369ac0f51e3f587366551939.
Even better gif detection
Replacing embedded GIFs is no longer in scope

It's unrealistic to build a Chrome extension to detect whether GIFs are
animated and when it's appropriate to convert them. Also, having the
extension modify pages creates a vulnerability to XSS exploits,
dramatically reducing security. JiffyGIF is now feature-complete.