remove kernel selector from header

- add kernel name to indicator (#6754)
- float kernel logo where selector dropdown used to be

IPython:

![screen shot 2014-12-09 at 15 28 34](https://cloud.githubusercontent.com/assets/151929/5368218/4c7f4e04-7fb8-11e4-8036-2402e7b9e1ed.PNG)

Julia:

![screen shot 2014-12-09 at 15 28 56](https://cloud.githubusercontent.com/assets/151929/5368222/5696b3d2-7fb8-11e4-8fbb-05e9205a395a.PNG)

Ping @ellisonbg and @Carreau, who were working on the kernel indicator design in #6754. This is my understanding of the current state of that discussion, but I don't think it was settled, and it should be easy to change.