#18: Added smaller dev-human logo to display on smaller sized displays t...

Trying to fix #18 by displaying a different logo on smaller screen sizes.

Currently, on smaller sized mobiles this is how the header is rendered:
![screen shot 2014-10-11 at 17 41 45](https://cloud.githubusercontent.com/assets/106844/4603239/7b6e6130-5161-11e4-879c-9406e2a5755a.png)

This is how it's rendered after the change:
![screen shot 2014-10-11 at 18 10 05](https://cloud.githubusercontent.com/assets/106844/4603240/82842bbc-5161-11e4-90f6-8dc8d3a82552.png)

There's still a lot of margin around the text, but I'll try to fix that in another PR.