re-structure Java API, add Scala API and consolidate the names of Java/Scala API

jvm-packages/xgboost4j-demo/LICENSE

@@ -0,0 +1,15 @@
+/*
+Copyright (c) 2014 by Contributors 
+
+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.
+*/