Some complexity is now gone. We didn't currently have a good justification
for a the APIHandler factory: the apiHandler caller would have to specify
(variable `foreign`) what kind of handler it would like to initiate anyway,
so it might as well just inject the object (which makes the code easier to
follow, decreases bugs risk because there are less code paths)
This also gives the caller more control of the API handlers:
registerForeignSources will now be able to do more. Now it can e.g. create
1 object that is shared for multiple wikis (to do lookups for multiple
wikis at once)
Also renamed addApiHandler to setApiHandler (it just sets the value it needs
without checking if it already existed anyway)
Change-Id: Ie1814c5bf1a1f0e5607033beb506df67f3585b24
876197b520