Harmonizing URI for examples

[agbeltran]

This PR includes

• changed the examples URI in the DCAT3 example files (under the /examples/vocab-dcat-3 folder)
• validated all the files
• changed the example URIs in the spec

Preview: https://raw.githack.com/w3c/dxwg/dcat-issue-1467/dcat/index.html

Diff: https://services.w3.org/htmldiff?doc1=https%3A%2F%2Fw3c.github.io%2Fdxwg%2Fdcat%2F&doc2=https%3A%2F%2Fraw.githack.com%2Fw3c%2Fdxwg%2Fdcat-issue-1467%2Fdcat%2Findex.html

[riccardoAlbertoni]

Thanks, @agbeltran for your efforts. This PR has already improved a lot the examples' consistency.

I have two observations:

• it seems that not all the RDF examples are updated. For example, basic-example.ttl still uses some  http://example.org/..., whereas this PR changes the correspondent part in the HTML. Have you pushed all the GIT commits you had in your local copy of the repository?
• In the HTML, we use ex:, :, and  a:, to refer to fictional example URIs. Moreover, in some cases, the namespace in the HTML is denoted by ":" in the HTML  corresponds to ex: in the RDF,  I wonder if we want to pick one among ":" or "ex" uniformize the examples in the HTML and RDF accordingly. 

[riccardoAlbertoni]

Thanks, I have noticed still some inconsistencies. Merging the PR #1497 should get rid of them.

[agbeltran]

thanks @riccardoAlbertoni - I'll have a look (but I am still going through the spec and examples and have uncommitted changes)

[agbeltran]

PR replaced by #1500