Test suite improvements w/app.php refactoring.

Sooooo I just looked into why and it looks like [I'm the one that introduced that requirement](https://github.com/there4/slim-test-helpers/commit/f5dda0c7b1060bde5d22bd585e093f21afdae202) into slim-test-helpers in the first place, because my IDE doesn't support `4.*` and I neglected to update the version before I pushed my changes up. I'll change that, but will have to do it in slim-test-helpers first.