Add sponsors to footer

Fixes #2063.

![bildschirmfoto 2014-11-30 um 13 13 38](https://cloud.githubusercontent.com/assets/5362483/5237630/e393135c-7892-11e4-8f57-19e656a46c1a.PNG)

![bildschirmfoto 2014-11-30 um 13 13 46](https://cloud.githubusercontent.com/assets/5362483/5237631/e734ea3a-7892-11e4-8bae-2d9700687dd7.PNG)