[EPIC] Improve documentation

[taorepoara]

• [Task] Improve JSON Schema to HTML generation components-api#138

Lenra app API

• [Task] Describe the Lenra app API. api#3
• [Task] Generate documentation for the Lenra app API api#2
• [Task] Add Lenra app API reference to the documentation docs#77

Lenra app REST API

Describe the REST API usable from the applications.

• [Task] Normalize the Lenra app REST API api#4
• [Task] Version the Lenra app REST API server#428
• [Task] Describe the Lenra app REST API api#7
• [Task] Test Lenra app OpenAPI file and router server#430
• [Task] Add the Lenra app OpenAPI reference to the documentation website docs#74

Lenra server REST API

Describe the REST API to manage Lenra application (used by the back-office and the Lenra client).

• [Task] Normalize the Lenra server REST API api#5
• [Task] Version the Lenra server REST API server#381
• [Task] Describe the Lenra server REST API api#8
• [Task] Test Lenra server OpenAPI file and router server#330
• [Task] Add the Lenra server OpenAPI reference to the documentation website docs#75

Lenra app configuration file

Describe the lenra.yml file in the app source code.

• [Task] Describe the Lenra app configuration file #150
• [Task] Generate automated documentation for the Lenra app configuration file #152
• [Task] Add Lenra app configuration file reference to the documentation docs#76