#589 - changed animation of sign in form

Old:

![2](https://f.cloud.github.com/assets/3904502/1574333/468e095a-513c-11e3-9ce8-70781dbc9b69.gif)

New:

![1](https://f.cloud.github.com/assets/3904502/1574327/1efcbbfc-513c-11e3-8ad4-6c1b36ee0af6.gif)