Group all copyright statements in a single file.

This gives a much clearer overview of the licensing.

It also shows there are some problems:
- Some files are under GPLv3 only
- Some files have no known license at all.

src/factory.h

@@ -1,5 +1,22 @@
 /* vim:expandtab:ts=2 sw=2:
 */
+/*  Grafx2 - The Ultimate 256-color bitmap paint program
+
+	Copyright owned by various GrafX2 authors, see COPYRIGHT.txt for details.
+
+    Grafx2 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; version 2
+    of the License.
+
+    Grafx2 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 Grafx2; if not, see <http://www.gnu.org/licenses/>
+*/
 #ifndef FACTORY_H__
 #define FACTORY_H__