Add to Duplicity support for working with items also

[Dan]

Duplicity should be able to work with pairs of items, and to do item merges. Too many duplicated items after flooders and bots have mass created millions of items by importing sitelinks. Mainly for items with only one sitelink this is feasible and needed. Make it possible to load in first column (left screen side) a basic item and in the second (right side) candidates to a target item for merge. As a input for items could be used also Pasleim's merge-project subpages.