When selecting a non-stable version, add a message this is version is "only for testing".

The stable version is set via the new environment variable stable_version. E.g.
stable_version=1.7

setup/server.py

@@ -53,7 +53,10 @@ def build_app(path):
 
     @app.context_processor
     def app_context():
-        return dict(versions=os.getenv("VERSIONS","master").split(','))
+        return dict(
+            versions=os.getenv("VERSIONS","master").split(','), 
+            stable_version = os.getenv("stable_version", "master")
+        )
 
     prefix_bp = flask.Blueprint(version, __name__)
     prefix_bp.jinja_loader = jinja2.ChoiceLoader([