Stop swimming against the tide and accept what most of the rest of
the world does.
While it adds an annoying depth to the actual source code, it makes
the root directory nicer (no more 'test-res' dirs), means we don't
have to override the gradle config, and makes it nicer to work in
IDEA 2016.1.
The logic to get a correctly typed setting given a class is
pretty general purpose, and will be useful elsewhere. Pull
it out of ConfigBinder and add some tests for it.