Startup page improvements

Added links, related content, tagline and join date, as requested in #330. Most is pretty simple, but related content is slightly more complex. In order to make it easy to do, I've created a new partial for the related content sidebar, which should auto-populate blocks etc. Other places which have related content could also use this, but I've not refactored it yet to do so. Still got logos to do on #330, but that needs API changes, so this could be merged now.

Example screenshot:
![screen shot 2014-06-25 at 12 01 36](https://cloud.githubusercontent.com/assets/3565/3384326/2118373c-fc58-11e3-93e0-3fc0039c1014.png)

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