[Spike] Split category display

Just a quick spike on including all the category types in the dropdown. I'm unfamiliar with this part of the code, so feedback is welcome.

It seems to be working. Catching a debugger in `OrganisationsController#search` yields the same params, looking like this...
![screen shot 2014-11-27 at 21 08 45](https://cloud.githubusercontent.com/assets/3466499/5221730/4a1ec190-767a-11e4-9206-cf31aafba084.png)
 Drop select looks like this ...
![screen shot 2014-11-27 at 21 09 16](https://cloud.githubusercontent.com/assets/3466499/5221733/64467388-767a-11e4-8e40-09d2cb35703e.png)