Merge branch '38-fix-survey-message' into 'dev'

fix missing message_type from survey message

Closes #38

See merge request !25

formats/survey.py

@@ -6,6 +6,12 @@
 survey_schema = {
     "type": "object",
     "properties": {
+        "message_type": {
+            "type": "string",
+            "description": "Type of message",
+            "example": "survey",
+            "enum": ["survey"],
+        },
         "timestamp": {
             "type": "string",
             "format": "date-time",