Affiliated Docs logo

Uses @kbarbary's configurable-logo branch to make the astro:query logo appear as below.

![image](https://f.cloud.github.com/assets/143715/292218/e07e38e6-931e-11e2-8b77-9f047c93675d.png)


Should not be merged until https://github.com/astropy/astropy/pull/824 is.