Add a visibility filter to the default scene picker
Add ability to set the region that the ZincWidget will use

It defaults to the default region for the context so the default behaviour
will not change.
Merge branch 'master' into fit-dev
Add tests
Add smoothing
Add a current region and propagate changes to ZincWidget.

This was intended to fix an issue with selection but it wasn't the right
thing to do for that. Leaving it in in case it is useful in future.
Tidy up comments and adjust temporary testing code