Replaced footer icons with svg equivalents

Small before:
![small-before](https://cloud.githubusercontent.com/assets/331790/4103399/54b6e36c-315b-11e4-8e22-af620ded7ada.png)
Small after:
![small-after](https://cloud.githubusercontent.com/assets/331790/4103400/54bf40de-315b-11e4-97aa-4d0201bd9ad2.png)

Large before:
![large-before](https://cloud.githubusercontent.com/assets/331790/4103396/43592f6c-315b-11e4-8f21-ede962f53fa7.png)
Large after:
![large-after](https://cloud.githubusercontent.com/assets/331790/4103397/435feeec-315b-11e4-8d9e-4eb43133e8c1.png)