Move wikibase.RepoApi{,Error} to wikibase.api

Change-Id: I77e7368cf0352884b6762b16a7557480be1f4e26
Move RepoApi{,Error} usages

Change-Id: I5515fb02f48255e5bb7e629655f6731f1ad84581
Merge "Move wikibase.RepoApi{,Error} to wikibase.api"
Merge "Move RepoApi{,Error} usages"