Added v104r3 release notes

ReleaseNotes/v104r3.md

+2019-02-20 Geant4 v104r3
+===
+This release is based on `GEANT4 r10.4.3`, uses `LCG 93` and `Geant4Files v104r1`.
+
+This version is released on `Sim10` branch.
+
+## Latest Changes
+
+#### LHCb production G4 Physics List option1NoApplyCuts
+**[MR !42] Set preferred graphics library to silence CMake CMP0072 warning.**