Refactoring play icon position.

Video play icon seems still a little bit off on smaller sizes so this PR is refactoring how we are calculating the position of play icon.

Before:
![screen shot 2014-11-24 at 11 03 00](https://cloud.githubusercontent.com/assets/2579465/5164108/f7dbd514-73ca-11e4-954e-27238c857634.png)

After:
Small size
![screen shot 2014-11-24 at 11 03 31](https://cloud.githubusercontent.com/assets/2579465/5164111/0090fd88-73cb-11e4-9615-812f7dd52549.png)

Large size
![screen shot 2014-11-24 at 11 02 15](https://cloud.githubusercontent.com/assets/2579465/5164115/0c420e42-73cb-11e4-803b-920a34e4594d.png)