Rename the private implementation to ConfigBinderImpl, and
make ConfigBinder itself an interface.

This shouldn't be exposed. Internal classes switch to using
the full class rather than the interface, so they can carry
on accessing the removed methods.

This is just an IntelliJ refactor, using EventBus in place of
DMDircMBassador whenever possible.

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.