Allow API versioning (#85)

* add api v3 partial support.

* fix codecs in env.

* fix default codecs.

* split files.

* add session stats for api v3.

* fix API token env.

* fix null array in json.

* add CORS.

* save api version to labels.

* irgnore api token env.

* remove duplicate api version.

* move api version to settings.

OpenApi.yml

@@ -467,6 +467,9 @@ components:
     RoomSettings:
       type: object
       properties:
+        api_version:
+          type: number
+          description: if not set, version is taken from neko_image
         name:
           type: string
           example: foobar