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

Session.cpp

@@ -1,3 +1,22 @@
+/*
+ * 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 <algorithm>
 
 #include "defines.h"
@@ -5,14 +24,14 @@
 #include "Source.h"
 #include "Settings.h"
 #include "FrameBuffer.h"
-#include "Session.h"
 #include "FrameGrabber.h"
 #include "SessionCreator.h"
 #include "SessionSource.h"
 #include "MixingGroup.h"
-
 #include "Log.h"
 
+#include "Session.h"
+
 SessionNote::SessionNote(const std::string &t, bool l, int s): label(std::to_string(BaseToolkit::uniqueId())),
     text(t), large(l), stick(s), pos(glm::vec2(520.f, 30.f)), size(glm::vec2(220.f, 220.f))
 {