Vectorized ✓ and ⨉'s on Rule List

The two icons were images and weren't retina compatible which means they look quite bad. I used the already included Font Awesome and switched them to vector files.

![screen shot 2014-08-23 at 7 48 32 pm](https://cloud.githubusercontent.com/assets/1449259/4022210/9cc2449e-2b20-11e4-810e-485f02560e0e.png)
![screen shot 2014-08-23 at 7 48 42 pm](https://cloud.githubusercontent.com/assets/1449259/4022211/9cc687b6-2b20-11e4-9140-62bcd5bb1abb.png)