Code warning cleanup and add GPL license header to all CPP files

MediaSource.cpp

@@ -1,6 +1,23 @@
-#include <glm/gtc/matrix_transform.hpp>
+/*
+ * This file is part of vimix - video live mixer
+ *
+ * **Copyright** (C) 2020-2021 Bruno Herbelin <bruno.herbelin@gmail.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+**/
 
-#include "MediaSource.h"
+#include <glm/gtc/matrix_transform.hpp>
 
 #include "defines.h"
 #include "ImageShader.h"
@@ -11,6 +28,8 @@
 #include "Visitor.h"
 #include "Log.h"
 
+#include "MediaSource.h"
+
 MediaSource::MediaSource(uint64_t id) : Source(id), path_("")
 {
     // create media player