Document SimPhoNy v4

[kysrpex]

• Change description on the welcome page.
• Reorganize and enhance introduction.
  • Add Quickstart tutorial
  • Update installation page
  • Remove "Fundamentals concepts" section.
  • Remove "General architecture" section.
• Reorganize sections dedicated to management and use of ontologies
  • New "Ontology management" section that agglomerates several pages.
  • Updated "Included ontologies" page.
  • Dedicated page for pico. Removed related content from "Utilities" page.
  • Updated "Working with ontologies" page and renamed to "Ontology packages".
  • Moved supported ontology languages and formats to a new dedicated page.
  • Removed YAML ontology format documentation, as it is not longed supported.
  • Removed "Introduction to ontologies" section.
  • Moved all pages from the "Working with Ontologies" sections to the usage guide.
• Update year on LICENSE and license.md.
• Change conf.py
• Minor bugfix in import_export.ipynb
• Minor change in index.md

[kysrpex]

Closing as it was split in several separate PRs.