Prov-WD: Document should be accessible

[Ole Streicher]

Hi all,

currently, the LaTeX document misses the names and the multiplicity of
the relations between classes in the text. They are only given in the
figures (PNG).

This makes it impossible to completely understand the document for a
visually impaired person who is not able to view the figures.

The names (and descriptions) of the relations were removed from the
document text during the change from the 2018 PR; this was however not
discussed within the working group. They should be restored, and the
multiplicity should be added there, so that the document text is a
complete description of the standard.

I don't know whether IVOA has a goal of being accessible; however in our
case I do not see why we should not have it accessible (and this
discussion is already several months old).

Best regards

Ole