Flask extensions should use IBlueprint interface.

Flask extensions can register more than just routes for the app. So
change the extension point from IRoutes, to IBlueprint, a very simple
interface that has one method `get_blueprint`, enabling extensions to
return Flask Blueprint objects to be registered with the Flask app at
start up.

ckan/config/middleware.py

@@ -35,7 +35,7 @@
 from flask_debugtoolbar import DebugToolbarExtension
 
 from ckan.plugins import PluginImplementations
-from ckan.plugins.interfaces import IMiddleware, IRoutes
+from ckan.plugins.interfaces import IMiddleware, IBlueprint
 from ckan.lib.i18n import get_locales_from_config
 import ckan.lib.uploader as uploader
 from ckan.lib import jinja_extensions
@@ -347,7 +347,7 @@ def hello_world_post():
     app.register_blueprint(api)
 
     # Set up each iRoute extension as a Flask Blueprint
-    for plugin in PluginImplementations(IRoutes):
+    for plugin in PluginImplementations(IBlueprint):
         if hasattr(plugin, 'get_blueprint'):
             app.register_blueprint(plugin.get_blueprint(),
                                    prioritise_rules=True)

ckan/plugins/interfaces.py

@@ -1566,3 +1566,11 @@ def get_resource_uploader(self):
         :type id: string
 
         '''
+
+
+class IBlueprint(Interface):
+
+    '''Register an extension as a Flask Blueprint.'''
+
+    def get_blueprint(self):
+        '''Return a Flask Blueprint object to be registered by the app.'''