[favicon] birth

Added a favicon for kibana. Our little piece of paper icon is cute, but we can do better.

before:
![image](https://cloud.githubusercontent.com/assets/1329312/5151615/e58aae5a-719d-11e4-8256-1bb1a8ae7ad6.png)

after:
![image](https://cloud.githubusercontent.com/assets/1329312/5151618/ea93f924-719d-11e4-8134-842962309e3f.png)