JVET-AC0139: Unified merge function and updated cfg settings

The code from https://vcgit.hhi.fraunhofer.de/XiangLi/VVCSoftware_VTM/-/tree/xlxiangli/vtm19-mergerf4 has been rebased to the current master. Software manual has also been updated.

Inter tests have been launched. Class D results are in line with the proposal. I will remove "Draft" after the results of RA class B-F, LD class C-F are confirmed.