Update license headers and add new licenses

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

Change-Id: I803e1abdc6f126d5251746422e16fff7463f2dff
Reviewed-by: Antti Kokko <antti.kokko@digia.com>
Reviewed-by: Tony Sarajärvi <tony.sarajarvi@digia.com>
Merge remote-tracking branch 'origin/5.4' into dev

Change-Id: I1167df7c6dd3fb394011cd98edaa84f868d41eaf