Always set check_same_thread=False in case of SQLite engines.

Platypush is heavily multi-threaded, and it can happen that some
transactions are handled in different threads - and consistency
is managed by the application itself.

platypush/plugins/db/__init__.py

@@ -39,6 +39,8 @@ class DbPlugin(Plugin):
         if engine:
             if isinstance(engine, Engine):
                 return engine
+            if engine.startswith('sqlite://'):
+                kwargs['connect_args'] = {'check_same_thread': False}
 
             return create_engine(engine, *args, **kwargs)