SEO: related keywords on tag pages

Adds related keywords to tag pages for SEO.

![screen shot 2014-07-22 at 15 24 17](https://cloud.githubusercontent.com/assets/1001642/3659205/fcce1040-11ab-11e4-8595-f2a3e2a34551.png)

![screen shot 2014-07-22 at 15 24 44](https://cloud.githubusercontent.com/assets/1001642/3659206/0079efe8-11ac-11e4-95b9-b3279628aef0.png)

![screen shot 2014-07-22 at 15 24 57](https://cloud.githubusercontent.com/assets/1001642/3659209/0837a932-11ac-11e4-851e-fdadd0177181.png)

My design skillz suck. Kat and Alex aren't available to look at it at the moment, though.
Again, to make the templates usable in IntelliJ. I think we should stop doing implicit imports, anyway, as even without IntelliJ, it makes it very difficult to know where functions, etc., come from, if you want to look up definitions.