Make MonthNameUnlocalizer aware of genitive month names

See Ic7a5797.

This includes a major rewrite of the method. Now it tries to
unlocalize longer strings first. This should avoid all possible
conflicts.

Change-Id: I232fd3b5433f04396c53eecf3ad49d025a84ee64
Merge "Make MonthNameUnlocalizer aware of genitive month names"