Making wb.Tooltip use wb.RepoApiError instead of custom object

Instead of a custom object containing the error information to be used for being displayed
in a tooltip, wb.Tooltip makes use of wb.RepoApiError objects now. Done some rearrangement
in the Resources file as well.

Change-Id: I47bdbf9ddb81d12d7de6a7517e92779479f7c484
wikibase.RepoApiError QUnit tests

Change-Id: If9301fd92e37812f652a37f2e02c3f0c44674fb6