refactor scheduler extender related API

- move extender related API from pkg/scheduler/api to pkg/scheduler/apis/extender/v1

- alias extenderv1 to pkg/scheduler/apis/extender/v1

- use NodeScore and NodeScoreList in non-extender logic

pkg/scheduler/apis/extender/v1/doc.go

@@ -0,0 +1,20 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// +k8s:deepcopy-gen=package
+
+// Package v1 contains scheduler API objects.
+package v1 // import "k8s.io/kubernetes/pkg/scheduler/apis/extender/v1"