Validators should detect/autorepair duplicate items in Lists

[frizbog]

There are a number of lists in the object model that arguably should not contain duplicated data. I use the phrase "arguably should not" because while the spec does not say these duplicates are forbidden or even wrong, it would make no sense.

Examples:

• Lists of Notes attached to most objects
• Lists of children in a FamilyChild (the same child should not be in the list twice)
• Lists of Multimedia attached to Individuals, Families, etc.

This is a compromise (in response to Issue #84) to avoid adding the memory overhead of using HashSets or LinkedHashSets instead of ArrayLists in the underlying data model (HashSet uses 28 bytes more per item than an ArrayList, and a LinkedHashSet uses 36 more bytes per item).

[frizbog]

I've started this work in v3-development branch

[frizbog]

Released in v3.0.0