Have some way to mark an incident as a duplicate

[srabraham]

We often end up with multiple IMS incidents for the same actual incident, and it would be nice to have a good way to close out one of those as a duplicate of the other.

There are many ways this could be achieved, so I'd just say that the gold standard would be something like:

1. user notices that incident 2 is really the same thing as incident 1
2. user marks on the incident 2 page that this incident is a duplicate of incident 1
3. IMS automatically resolves incident 2 in some closed state
4. IMS automatically comments on both incidents indicating what happened (providing links in both lists of incident details from the one incident to the other)

[srabraham]

We'll probably just achieve this the simplest way, by adding a new Incident Type of "Duplicate"