Initial support for supplying kernel logos in kernel spec

![screenshot from 2014-09-24 11 58 38](https://cloud.githubusercontent.com/assets/327925/4393978/dddf862a-441c-11e4-8475-339c32e0a5f6.png)

Commence UI debate ;-)
@dsblank can you try to change `"/kernelspecs/"` -> `this.notebook.base_url+"kernelspecs/"` here ?