Bump MODULE_VERSION to 5.1.1

Change-Id: I9b0c63863a4c1914f15bdbba6c02758622403ed9
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Merge remote-tracking branch 'origin/release' into stable

Change-Id: Ie3ca435442bcaab4d77fee973b82967741055628