establish strict versions and last updated date

[VladimirAlexiev]

Accurate version numbers and last update are fairly important for efficient ontology use.
But we are very lax about them:

• The main ontology https://ci.mines-stetienne.fr/aec3po/ has no date or version
• Module ontologies eg https://ci.mines-stetienne.fr/aec3po/conformance_report have date but no version.

But the date is not updated! If you do "git blame" on that module, you see (@maximelefrancois86):

The declared dct:modified is not bumped to the last update.
(And the commit comment is too light to the actual changes made, but that's a secondary issue).

My proposal is to:

• for each module: strictly update dct:modified on every change
• for main:
  • have a global version, start at 1.0.0 and increment on every change of every module. (We should use https://semver.org principles, but I don't know whether we'd have major changes in the future)
  • strictly update dct:modified on every change of every module