Add a method to distinguish sites that are at the same location

When two locations are identical, save for the sub-location, we should show them slightly differently. More specifically, if the following is true:

1. Location A and Location B have the same address.
2. Location A and Location B have different sub-location names.

Then, Location A and Location B should be shown (somehow) as the same location, but with indented sub-location attributes.

No file or test is named. Start by locating the code that compares or renders locations, then define and verify the duplicate-address and distinct-sub-location presentation described here; done means identical addresses are grouped while differing sub-location names are indented.

Written by the indexing model from the issue text.