Add deduplication mechanisms

[cecilia-donnelly]

• We can do some automatic deduplication, especially by offering completion on names, but users will always have to do some manual work too. For people with same name, they often use phone number as the disambiguator.
• Users will run a report or similar tool to find potential duplicates and resolve them by merging or marking "not duplicates."
• For cases where we can’t know for sure which person (of two or more people with the same name) attended a given Action, we are thinking of adding a placeholder/shell person (“Mary Gonzales”), who is flagged as a meta-version of the multiple people with that name. To be discussed!

[cecilia-donnelly]

This came up again in our meeting with users on [2017-10-25]. @pjsier @kfogel

[kfogel]

The exact examples from the 2017-10-25 meeting were a duplicate Action, and some duplicate Participants in an Institution. I believe the Event was:

• "Action Council, St Casimir, Auditorium"
• Action Council, St Casimir Auditorium" (note lack of comma)

And the duplicate Participants were under the institution "Eberhard" (not putting the exact Participant name here, obviously).

They would both make good import/input dup-detection test cases.