Adde license to the ImageButton

issue A24Group/Triage#1933

src/org/ssgwt/client/ui/ImageButton.java

@@ -1,3 +1,16 @@
+/**
+ * Copyright 2012 A24Group
+ * 
+ * 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. 
+ */
 package org.ssgwt.client.ui;
 
 import com.google.gwt.dom.client.Document;