Freshly baked Slapdash app should come with basic integration tests

Slapdash comes with some round-trip tests to verify that the cookiecutter recipe, when baked, will successfully create a functioning Dash app and eg its multi-page routes work. 

The recipe should be enhanced so that after baking your app, it comes with analogous smoke tests so that you can verify your app at least runs and all expected routes are accessible. 