Organisations on subsector pages (not ready for merge)

This implements https://www.pivotaltracker.com/story/show/75807888, which adds a list of organisations which are related to the content in a specialist sub-sector.

Looks like 
![screen shot 2014-08-08 at 10 45 27](https://cloud.githubusercontent.com/assets/73564/3855145/d51d9ed4-1ee0-11e4-80dd-c68fc449f778.png)

I don't think this is true as a general rule, as different steps can be implemented in the same way as an implementation detail.

In this case, however, it seems like the organisation stubbing probably shouldn't be the default behaviour of `stub_specialist_sector_topics` without being requested.