Create a taxonomy linter and lint properties

[alexgarel]

We have several problems we can solve at once:

• if a property is named after an existing taxonomy we would like to replace values by normalized values corresponding to id of entry in referenced taxonomy (because it is hard to do at taxonomy build time)
• we want to avoid having more than one line per language for one entry
• we want to avoid git auto merges to join two distinct entries
  • this can be detected if more than one line for same language (see above)
  • or if we have a < in the middle of an entry
• we would like to keep taxonomies sorted (in the near future)

For that we need a taxonomy linter than can act in modify or check mode.