Added Flask config for custom JSON encoder

Author: jtc42

src/labthings/server/representations.py

@@ -35,7 +35,7 @@ def output_json(data, code, headers=None):
     """Makes a Flask response with a JSON encoded body, using app JSON settings"""
 
     settings = current_app.config.get("LABTHINGS_JSON", {})
-    encoder = LabThingsJSONEncoder
+    encoder = current_app.config.get("LABTHINGS_JSON_ENCODER", {}) or LabThingsJSONEncoder
 
     if current_app.debug:
         settings.setdefault("indent", 4)