SpecialMergeItems shoudl be rewritten to use ItemMergeInteractor. Also, logic currently inherited from SpecialWikibaseRepoPage and SpecialWikibasePage should be factored into helper components.

Merging items can and should be made into an example of sharing logic between API and special pages.

Version: unspecified
Severity: major
Whiteboard: u=dev c=backend p=0