Update license headers and add new license files

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

Change-Id: I4852e1e3fb306319e63d919675acad9a64e43db6
Reviewed-by: Jani Heikkinen <jani.heikkinen@digia.com>