If there's no notification, we have to fallback to the treeview's
foreground colour instead of hardcoding black...

Closes #503

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

These interfaces are basically pointless.

Window only has a getContainer() method, so we may as well just
pass a WindowModel around instead.

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.