Update license headers and add new licenses

- Renamed LICENSE.LGPL to LICENSE.LGPLv21
- Added LICENSE.LGPLv3 & LICENSE.GPLv2
- Removed LICENSE.GPL

Change-Id: I99c601a398559886c2900f3e04833acfceba8263
Reviewed-by: Antti Kokko <antti.kokko@digia.com>
Reviewed-by: BogDan Vatra <bogdan@kde.org>
Reviewed-by: Tony Sarajärvi <tony.sarajarvi@digia.com>