Add ability for app.static() to return the routes it created. (#1954)

This allows blueprint registration to add the bp's static routes to its list of own routes. So now blueprint middlewares will apply to a blueprint's static file routes.
Fixes #1953

sanic/app.py

@@ -676,9 +676,10 @@ class Sanic:
         :param strict_slashes: Instruct :class:`Sanic` to check if the request
             URLs need to terminate with a */*
         :param content_type: user defined content type for header
-        :return: None
+        :return: routes registered on the router
+        :rtype: List[sanic.router.Route]
         """
-        static_register(
+        return static_register(
             self,
             uri,
             file_or_directory,