Prepare for next development iteration

Change-Id: I796b4e179127f41e078378472083321161606eea
debian/control: Add libgnutls28-dev to debian build dependencies

Change-Id: Ic4b84e5aaed34f639ed9ef2d45f73154768b7c49
Prepare release 5.0.4

Change-Id: I948a9f4d2cdd7b915be9fb92d630712e4317a74e