Update license headers and add new license files

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

Change-Id: If9208b9c90bcea35bbfe6b9c10db7803e97767e0
Reviewed-by: Jani Heikkinen <jani.heikkinen@digia.com>