[META] New documentation and new organisation

This is a meta issue listing all the changes before releasing the new documentation.
The current version of this MR is visible : http://cubicweb.pages.logilab.fr/cubicweb/dev/

If you want to work on one of the issue listed below, tag yourself in the corresponding issue and create a merge request with dev-doc as destination branch.

• #76 (closed) - create a new tutorial (for the 3.30)
• #77 (closed) - restructure /book/devrepo/cubes/layout.html !55 (merged)
• #78 (closed) - create page «what is a cube?» !51 (closed)
• #82 (closed) - update data model to mention regexp !54 (merged)
• #83 (closed) - add reference to the heptapod reference !52 (merged)
• #84 - add an example to add a new workflow
• #115 (closed) - Add __init__.py description
• add new issue here ;)

New plan :

• Cubicweb core principel
  • Cubes
    • - Write Cube skeleton
  • The Registeries
    • - Write All available registries
• Routing
  • Principle
    • - Write CubicWeb and Pyramid
    • - Write The CW request object
    • - Write `encapsulation of the CW request in the pyramid request
    • - Write bw_compat and the options to use, fallback when CW dosen't find anything -Pyramid routing
    • - Write general principles
    • - Write predicates
    • - Write tweens
    • - Write content negociation
• Front development
  • With Jabascript / Typescript (using React)
    • - Write general principle
    • - Write how to install and integrate js tooling into CW
    • - Write cwelements
    • - Write rql browser
  • With pyramid
    • - Write general integration with CubicWeb
    • - Write the renderers
    • - Write example of usages with CW
  • With CubicWeb Views
    • - Write Facets
    • - Write How to use javascript inside CW views
    • - Write Customize CSS
  • RDF
    • - Write the RDF adaptor
    • - Write RDFLib integration into CW
• Data model and management
  • Importation
    • - Write massive store
• Security
  • Security
    • - Write Permissions management with Pyramid
• Migrate your schema
  • Migration
    • - Write Write script migration
    • - Write Execute script migration
    • - Write Debug script migration
• CubicWeb configuration files
  • Base configuration
    • - Write The all-in-one.conf
• Developpement
  • Debugging
    • - Write Command line options for debugging
    • - Write Debugging configuration directly in the code
    • - Write Pyramid debug toolbar
    • - Write Debug channels
  • Good practices
    • - Write tox
    • - Write check-manifest
    • - Write mypy
    • - Write flake8 and black
  • CI
    • - Write Gitlab-ci integration
• System administration
  • Deployment
    • - Write Raw python deployment
    • - Write Working with Docker
    • - Write Working with Debian packages
  • Administration
    • - Write the cubicweb-ctl tool
    • - Write sources configuration
    • - Write backup
• - Write logilab-constraints
• - Write logilab-mtconverter
• - Write How to contribute