Once Stripes has a notion of which back-end interfaces are present and at what version (
STRIPES-399) we will be able to compare this list with the set of requirements expressed in the `stripes.okapiInterfaces` part of the modules' `package.json` files, and determine which required interfaces are absent or available only at incompatible versions. We can then warn the user if there is a problem (or simply refuse to run).
For maximum flexibility, we may wish to extend the `package.json` dependency syntax so it can express which dependencies are mandatory (e.g. ui-users' dependency on the users interface) and which are only desired (e.g. its dependencies on the circulation and permissions interfaces.)