GH-1876 Clarify license of GroupView

The LGPL code that came from KDE has been removed back in 2014.
It was replaced with a different implementation, made in
a separate repository.

See commits:
a17caba2c9
b82eb5873e

application/groupview/VisualGroup.cpp

@@ -1,3 +1,18 @@
+/* Copyright 2013-2017 MultiMC 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.
+ */
+
 #include "VisualGroup.h"
 
 #include <QModelIndex>