Add GPL headers to all source files

src/ag-window.c

@@ -1,3 +1,21 @@
+/* ag-window.c - Main window management for Astrognome
+ *
+ * Copyright (C) 2014 Polonkai Gergely
+ *
+ * Astrognome 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.
+ *
+ * Astrognome 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 software; if not, see
+ * <http://www.gnu.org/licenses/>.
+ */
 #include <math.h>
 #include <string.h>
 #include <glib/gi18n.h>