Set a need to be a duplicate of another
Need can not be a duplicate of itself
Simplify duplicate validation
Extract duplicated code to test helper
Need can't be a duplicate of a need that is itself a duplicate
Move duplicate needs tests to a new context
Main need points to a closed need
Remove duplicate needs test setup duplication
Authoritative need can have multiple duplicates
Default duplicate_of field to nil
Needs can't have chains of duplicates
Tidy up tests
Move test to more general context
Add controller code for closed action

Update routes. Add integration and functional tests.
Add 'close' action to Need Revisions.

Make action parameter explicit and update tests accordingly.
Integration test to check action type is 'close'
Switch order of parameters for
WIP avoid copy/paste duplication from spreadsheets