Adding and removing claims now shows a full diff

Until now if you added a new claim or removed a claim
the diff would only show the mainsnak.
This change means the whole claim appears in the diff
when it is removed.

This also adds test for the ClaimDifferenceVisualizer
There were no tests actually running in this class
before as they were commented out...

We also remove a functions that is no longer used

Bug: 53142


Change-Id: Ib8709a7b5a1cc3e2ba32bc9057154ced1ff2d334
Merge "Adding and removing claims now shows a full diff"