Investigate compatibility between various servers and existing Solid apps

[michielbdejong]

It has been reported that

The majority of implementations that pass the table are not compatible with existing apps.

Let's investigate this claim and make sure that whenever an existing app from https://solidproject.org/apps works against server A but not against server B, we find out where the incompatibility stems from, and investigate whether that is:

1. something that is required by the spec or
2. described by the spec as optional, or
3. not described by the spec at all and just a result of over-fitting to the behaviour of server A.

In case 1 we should make sure a test exists, and file a bug about it against server B.
In case 2 we should also make sure a test exists, and file a bug about it against the app in question, trying to help the app developer navigate their way around optional parts of the spec.
In case 3 we should file a bug against the app and/or against maybe some upstream dependency of it (rdflib, Inrupt SDK, etc).