#968 Clarify differences in moderator merge approval screen

[Anonymous]

Improve the moderator approval screen for title merges to make it clearers which fields are different and which are the same.

The screen showing for the merge submission (see Merge-Submission figure attached) clearly shows which fields are the same and which fields are different (and allows user to select ones to keep). However, the associated moderator approval (see Merge-Approval figure attached) forces the moderator to compare each field for differences. In the example, only the storlen fields are different.

To make it easier & less unlikly to miss small changes, the moderator approval should make it easy to see what fields are actually different. Suggestions for doing so are:
1. If both sides of a row are the same, make both sides green
2. If both sides of a row are the same, span the row across both columns, show one value, and make green

[Ahasuerus]

Implemented in common/viewers.py 1.123. Installed in r2016-218 on 2016-12-28. Closing.