Add license header to ExternalLibrary class.

Author: BenDol

src/main/java/gwt/material/design/demo/client/application/datatable/contextmenu/ContextMenuDataTableModule.java

@@ -20,7 +20,6 @@
  * #L%
  */
 
-
 import com.gwtplatform.mvp.client.gin.AbstractPresenterModule;
 
 public class ContextMenuDataTableModule extends AbstractPresenterModule {

src/main/java/gwt/material/design/demo/client/ui/ExternalLibrary.java

@@ -1,5 +1,25 @@
 package gwt.material.design.demo.client.ui;
 
+/*
+ * #%L
+ * GwtMaterial
+ * %%
+ * Copyright (C) 2015 - 2016 GwtMaterialDesign
+ * %%
+ * 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.
+ * #L%
+ */
+
 import com.google.gwt.dom.client.Document;
 import gwt.material.design.client.base.MaterialWidget;
 import gwt.material.design.client.constants.IconType;