Userinfo provider

* userinfo api requests are cached now
* we use jsonp only if we have to (makes gender api calls measurable on WMF wikis)
* all API calls use providers now, provider.Api constructor can be used to
  wrap mw.Api with metrics

Does not return a proper model, and gender API calls are not preloaded together
with the rest of the calls. Maybe next time.

Change-Id: I9b3ea73c65eef57e160ac8636d9e45d349150884
Merge "Userinfo provider"