Merge lp://staging/~teemperor/pantheon-greeter/slide-away-ui into lp://staging/~elementary-pantheon/pantheon-greeter/trunk

I'm not a huge fan of the login box and clock sliding away. I think it would be better if they used the same animation as a window closing. But overall, it's an improvement to have some kind of animation here.

Actually it might not be an improvement because the animation is rather long (in time) and will end abruptly in case of fast login. This will not look good.

I would prefer a shorter animation where the clock and login box slide out in different directions but fade out quickly, before they leave the screen. This would look as if they're revealing the desktop, which I believe was your original intention, but will be much shorter.

I'm not a fan of using the window closing animation here, it doesn't give the sence of entering your workspace or anything like that, it feels like just some annoying boxes getting out of your way.

My assumption about animation ending abruptly was wrong - turns out the greeter completes the animation first and then initiates the user session. So the login will always be delayed by the length of the animation, 600ms in this case, which IMO is unacceptable. If we choose to implement animation at all, it should be no longer than 200ms.