Add --no-run parameter

This parameter allows e.g. to synchronize the database without starting
the webserver.

openslides/main.py

@@ -101,6 +101,9 @@ def process_options(argv=None, manage_runserver=False):
         "--no-browser",
         action="store_false", dest="start_browser", default=True,
         help="Do not automatically start web browser.")
+    parser.add_option(
+        "--no-run", action="store_true",
+        help="Do not start the development server.")
     parser.add_option(
         "--version", action="store_true",
         help="Show version and exit.")
@@ -187,6 +190,9 @@ def _main(opts, database_path=None):
     elif opts.reset_admin:
         create_or_reset_admin_user()
 
+    if opts.no_run:
+        return
+
     # Start OpenSlides
     reload = True
     if opts.no_reload: