Introduce a deprecated flag on props and schemata

[pudo]

This creates a mechanism for warning users that a given schema or property will be removed in the future and should no longer be used.

I'm not sure where all the places are that we would want to check and alert this - probably want to keep it a bit limited in order to avoid nasty levels of noise and a perf impact.

[tillprochaska]

It would be great to add this to the to_dict methods (so it is included in the model JSON) and ideally to the TS lib, too, so we can display a warning in the model explorer and hide deprecated schemata in the Aleph UI (or at least prevent users from creating new entities using deprecated schemata).

[pudo]

I assume this would be really nice to feature in SchemaPageHeader, perhaps as an alert box? Maybe I can ask your help for that?

[tillprochaska]

Yep, I’ll add it to the docs. Will do that in a separate PR though so this one isn’t blocked. Also, this feature needs to be in a release of the TS lib in order to use it in the docs :)

[pudo]

Agree that linking hidden and deprecated was sketch :)

[tillprochaska]

Nice, thanks!