Add algorithm for determining primary record in duplicate

[oubiwann]

This should probably be something on the order of:

• Check that records in group are actually duplicates (according to fields specified for uniquing)
• Check which one is the most recently updated (this should the primary tie-breaker)
• Check which one has the highest access count (this should the secondary tie-breaker)
• If the status differs between two, select active status (tertiary tie-breaker)

Tasks:

• Revisit password history abstraction
• Add Column::DuplicateInfo (bool)
• Include in duplicate listing output
• Add support for post-processing duplicate records
• Include history counts when processing records
• When listing duplicates, in the "Duplicate Info" column
  • set one as primary
  • check to see if the others are identical to existing password history items, and if so, set as in history
  • set all others as duplicate

Part of:

• Support sensible record de-duplication #103