Added SimpleConnection to relay types

Sometimes you do not want a full blown relay connection, where you have `edges[...].node.attribute` but simply `edges[...].attribute`. According to https://github.com/graphql/graphql-relay-js/issues/27#issuecomment-142421989 relay has support for this simpler use-case as well if you do not need certain functionality such as deletion. This implements such a type that can be used instead of the default connection via the `connection_type` argument on `ConnectionField`

graphene/relay/types.py

@@ -103,6 +103,35 @@ class Connection(ObjectType):
         return self._connection_data
 
 
+class SimpleConnection(Connection):
+    '''A connection without nodes to a list of items.'''
+
+    class Meta:
+        type_name = 'SimpleConnection'
+
+    @classmethod
+    @memoize
+    def for_node(cls, node, edge_type=None):
+        from graphene.relay.utils import is_node
+        edge_type = edge_type or node
+        assert is_node(node), 'ObjectTypes in a connection have to be Nodes'
+        edges = List(edge_type, description='Information to aid in pagination.')
+        return type(
+            '%s%s' % (node._meta.type_name, cls._meta.type_name),
+            (cls,),
+            {'edge_type': edge_type, 'edges': edges})
+
+    @classmethod
+    def from_list(cls, iterable, args, context, info):
+        assert isinstance(
+            iterable, Iterable), 'Resolved value from the connection field have to be iterable'
+        connection = connection_from_list(
+            iterable, args, simple_list=True, connection_type=cls,
+            edge_type=cls.edge_type, pageinfo_type=PageInfo)
+        connection.set_connection_data(iterable)
+        return connection
+
+
 class NodeMeta(InterfaceMeta):
 
     def construct_get_node(cls):