Force a new writing system id when duplicating

Duplicating an existing writing system in the UI, then deleting the
duplicate would result in deleting the original writing system since
the duplicate has the same id with a simple Clone based duplication.
Looking at the summary in libpalaso/Palaso/WritingSystems/WritingSystemRepositoryBase.cs, it looks like MakeDuplicate() is intended to keep the same Id (for editing).

Still, It seem like this should be a method of WritingSystemRepositoryBase and not in the user of the class.  Add a new method?