Add JSON editor and JSON Schema validation

Add JSON editor and JSON Schema validation

• Editor: https://github.com/josdejong/jsoneditor (to be installed manually in /libraires for now to test)
• JSON Schema validation (PHP): https://github.com/swaggest/php-json-schema

Adds a new form widget using jsoneditor
The JSON schema is defined in the form widget configuration (the same field could be use for different type of data)
Settings to prevent saving the entity if the data doesn't follow the defined schema

Details to be added later