Respect html_logo, and throw it in the sidebar, fixes #24

This basically fixes issue #24, and lets users' html_logo choice get put in the sidebar, underneath the little house logo and title (looks best there, I think). Not sure if we also wanna do something like hide the actual text title if there's a logo, too?

Examples:
![screen shot 2013-12-08 at 10 20 20 pm](https://f.cloud.github.com/assets/251281/1700266/afe46892-6003-11e3-9936-ffd20f685cc3.png)
![screen shot 2013-12-08 at 10 21 32 pm](https://f.cloud.github.com/assets/251281/1700267/b19f62fe-6003-11e3-9836-d284fc7ebbe6.png)

It also shrinks to fit how large or small the sidebar is. For example, if the sidebar is only 50px wide, the logo image will shrink to fit.