send parent window url in startHypothesis message (#461)
send parent window url in startHypothesis message (#461)

* MFR overrides the hypothes.is annotator to send the parent window's
   url. It had been doing this by calling `document.referrer` in the
   child iframe, but to improve privacy browsers have started making
   only the parent window's domain available to the child. The child
   no longer has access to the full path.

   To get around this, the parent window will now send along its full
   url with the `startHypothesis` message it sends to the child
   iframe. MFR has been updated to receive and store this url and to
   use it to identify comments when submitting to the upstream
   service.
CenterForOpenScience/ember-osf,CenterForOpenScience/ember-osf