Only register gdrive callback if gdrive is enabled

With enabled gdrive return on change if no watch callback is configured, instead of send request to google drive

cps/gdriveutils.py

@@ -20,6 +20,8 @@ from __future__ import division, print_function, unicode_literals
 import os
 import json
 import shutil
+import chardet
+import ssl
 
 from flask import Response, stream_with_context
 from sqlalchemy import create_engine