[schemas] add a note for human readable item documentation

[e-maud]

e.g. in case of weird stuff that we change such as 31.04.1892

Name: 'note' ?

[simon-clematide]

We got rid of the wrong date and the corresponding correction was applied down to the PDFs that we derive everything from. Where would you want to add this actually?

[mromanello]

You mean a note property in the issue.schema, right ? I agree that we should record it somewhere, and if we put it there we can then propagate it into DB and/or Solr. Ultimately, I think, there should be a way to display this somewhere in the UI (ping @danieleguido) for the sake of generosity and transparency about data etc.

[e-maud]

Yes, the idea was a bit to record whatever extra/weird unexpected change we are doing on the data, independently from automatic parsing. Just to record and eventually display in the interface. E.g. the user would understand why the image 31.04 is displayed under the identifier 01.05.
Issue would be the right level to encode this info, yes, and then moved on to rebuilt/solr/DB down to user.