[doc] Restructure the documentation
* Create a new index file
* Move the sphinx configuration files do the documentation root
* Move book/README to dev/documenting.rst
* Move book/mode_plan.py to tools/
* Move book/en/images to images
* Move book/en/* to book/
* Move changelogs to changes/*
* Adapt the Makefile
* Add a title to the javascript api index
Related to #4832808