Licenses: Change WTFPL to MIT (part 2)

Add license.txt files.
Update and improve README.txt files.
Corrections to part 1.

mods/walls/license.txt

@@ -1,5 +1,7 @@
 License of source code
 ----------------------
+
+GNU Lesser General Public License, version 2.1
 Copyright (C) 2016 sofar (sofar@foo-projects.org)
 
 This program is free software; you can redistribute it and/or modify it under the terms