Slider axis vertical

![vertical-slider](https://f.cloud.github.com/assets/55838/1219063/efecd320-26c4-11e3-8565-394a47e29bd5.png)

Original pull request: https://github.com/montagejs/digit/pull/23
(It needed to be manually rebaselined with a master so I didn’t know how to continue with the existing pull request. Maybe my git-fu is not good enough)