Automatically / routinely check compatibility of latest app versions

Since apps can now define their own requirements, you will inevitably end up with conflicts.

There is no great solution to this, but one thing that would make sense to me is:
whenever you update the aiidalab app registry, also run a job that
1. collects the requirements of the latest versions of all registered apps
2. tries to figure out whether these requirements are compatible

Ideally, step 2 could be done without actually having to install those requirements.

@csadorf mentioned one could try this with a `Pipfile`

Otherwise there is [`pip check`](https://pip.pypa.io/en/stable/cli/pip_check/) but I think that only works if you actually install all of the apps.

P.S. There is also [`pip download`](https://pip.pypa.io/en/stable/cli/pip_download/) which does the same resolution as `pip install` but just downloads the packages (and should thus be faster)