revise primary_ble_sensed_mode_for_trip again for JS

As it turns out, Transcrypt doesn't support the 'index' argument of the max() function, so we cannot use the preferred Python method here.
We'll have to make our own little for-loop to find the max. Finally, this works in JS as well as Python!

src/emcommon/bluetooth/ble_matching.py

@@ -74,12 +74,16 @@ def get_vehicle_with_ble_beacon(major_minor, app_config):
     Logger.log_debug('no vehicle found for BLE beacon %s' % major_minor)
     return None
 
-def primary_ble_sensed_mode_for_trip(trip: dict) -> str:
+def primary_ble_sensed_mode_for_trip(trip) -> str:
     """
     Returns the primary BLE sensed mode for the trip (the mode with the greatest distance).
     """
     if 'ble_sensed_summary' not in trip or 'distance' not in trip['ble_sensed_summary']:
         return None
     dists = trip['ble_sensed_summary']['distance']
+    dists = dists if type(dists) == dict else dict(dists)
     # return the key of the mode with the greatest distance
-    return max(dists, key=lambda mode: dists[mode])
+    high = (None, 0)
+    for k, v in dists.items():
+        high = (k, v) if v > high[1] else high
+    return high[0]