Command map-master name should be changed

[pmuilu]

map-master is a bit confusing name. mv-master could describe the behavior better.

[pmuilu]

mv-master could actually behave a bit similarly as git mv, i.e. it would also do the local operation. We could then just deprecate the map-master command altogether. Additionally, it could provide --keep-locale-map so it won't reset the mappings.