Add categories to applications and enable searching by them

This PR:
- Refactors the processing of applications from PublishMyData in a nice
  library class and adds a whole bunch of tests for it
- Tidies up a few bugs and niggles in the ApplicationClassifier
- Tidies up the location of the classifer and processor to be Hampshire-specific
- Uses the classifier and some other logic to add categories to applications
  whilst importing them
- Makes the list of categories configurable
- Wires up the search controller to identify categories as something special
  and use a facet to allow you to search by them

And now I will rebase it so the mess of commits actually reads something like
the above

Closes #31