Renaming/fixing of content-item schema

[piconti]

The Content-item schema is meant to represent the rebuilt content-items, but it's not very clear of explicit and it might be outdated. It should be updated and made more clear.

In addition, as pointed out by @simon-clematide, the porperty "t" is present twice in the schema, both for title and token.
It's not at the same level of the schema hierarchy, so it has currently not caused too many issues, but is not ideal and should probably be changed.

Action points for this issue are thus:

• Making it more explicit that the content-item schema corresponds to the rebuilt, potentially by renaming the schema
• Ensuring it is up to date and still aligned with the actual content of the rebuilt data
• Renaming the title or token property, once it has been modified in the data.