API list=alltransclusions, rm unique+gen & continue restrict

API list=alltransclusions, rm unique+gen & continue restrict

* list=alltransclusions added to enumerate every instance of page embedding
* list=alllinks & alltransclusions now allow both 'from' and 'continue' in
  the same query. When both are present, 'from' is simply ignored.
* list=alllinks & alltransclusions now allow 'unique' in generators, to yield
  a list of all link/template target pages instead of source pages.

Change-Id: I4137e2d790f988e0cef638703d9d6961a47fe662