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.

Use @Nonnull

These are from the TextPane, but seem fairly general purpose.

Change-Id: Ic119eb461a365b4f7050715c6bc0abd5c034e57c
Reviewed-on: http://gerrit.dmdirc.com/4081
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager