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

Connection.cpp

@@ -1,3 +1,21 @@
+/*
+ * 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 <thread>
 #include <chrono>
@@ -147,7 +165,7 @@ int Connection::index(ConnectionInfo i) const
 
 void Connection::print()
 {
-    for(int i = 0; i<connections_.size(); i++) {
+    for(size_t i = 0; i<connections_.size(); i++) {
         Log::Info(" - %s %s:%d", connections_[i].name.c_str(), connections_[i].address.c_str(), connections_[i].port_handshake);
     }
 }