server: SàT applications integration: - a SàT Application can be added to the menu (if necessary values are exposed), by using the `sat-app:[application_name]` in `menu_json` or `menu_extra_json`. The application will then be started with Libervia, and embedded, i.e. Libervia menu will appear and application will be integrated under it. - the same `sat-app:[application_name]` thing can be used in redirection, in this case the redirection will reverse proxy directly the application, without embedding it (no Libervia menu will appear) - the ReverseProxy will replace headers if necessary to allow embedding in a iframe from the same domain - new `embed_app` page to embed a SàT Application