Code review comment for lp:~lifeless/launchpad/databasefixture

Thanks jml; turns out its got furrther (shallow) changes needed to not
break things (ProcessLayerController needed some love). This doesn't
help (or hinder) your point 2. I think that wanting a composite is
fair, but we'd want to be able to inspect the innards anyway which
somewhat defeats having a composite. For now, I think treating
BaseLayer as that composite itself isn't unreasonable.