Call update_device_chats automatically during configure (#1957)

update_device_chats() takes about 2 seconds on a modern device (Android) because the
welcome image file has to be written to the disk as a blob. The problem
was that this was done after the progress bar had vanished and before
anything else happened so that I thought that something had gone wrong
multiple times.

The UIs have to remove update_device_chats(), too..

python/src/deltachat/testplugin.py

@@ -354,6 +354,8 @@ def acfactory(pytestconfig, tmpdir, request, session_liveconfig, data):
             for acc in self._accounts:
                 if hasattr(acc, "_configtracker"):
                     acc._configtracker.wait_finish()
+                    acc._evtracker.consume_events()
+                    acc.get_device_chat().mark_noticed()
                     del acc._configtracker
                 acc.set_config("bcc_self", "0")
                 if acc.is_configured() and not acc.is_started():