Separate promote page

 - Improved tweet text
 - Moved share buttons and promotion list to new page
 - Fixed layout of buttons on contribute page

![screen shot 2014-07-02 at 23 20 56](https://cloud.githubusercontent.com/assets/660805/3463228/2b607080-0237-11e4-8698-d186a060d678.png)
![screen shot 2014-07-02 at 23 20 48](https://cloud.githubusercontent.com/assets/660805/3463230/2cc46fb2-0237-11e4-8d26-10cc84d78ff8.png)