Bump MODULE_VERSION to 5.1.1

Change-Id: If1f625bf9ff5819bb2d82f8a46178c1935588e6f
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Merge branch 'release' into stable

Change-Id: I07228275ddc3cb515d11eca4b3f5ea4671c9edc4