Apply ASF licenses throughout the code base (#5800)

* Add license headers

* reabased

* lint

* Removing licenses from vendors folder

superset/assets/spec/javascripts/explore/components/DisplayQueryButton_spec.jsx

@@ -1,3 +1,21 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
 import React from 'react';
 import { mount } from 'enzyme';
 import ModalTrigger from './../../../../src/components/ModalTrigger';