Adapt to PDF.js v1.0.68. Touches #71.
TextRange: handle an error case
PDF plugin: use native HTML5 Promise

... instead of the promise implementation that used to be bundled
with PDF.js, but was removed for v1.0.277.

Solves #69.
Add support for PDF url and fingerprint detection

1.

Now the PDF plugin is able to properly detect the
URL and fingerprint of the PDF document being viewed
by PDF.js.

However, this support is not leveraged by Annotator core,
for now. (It's up the the application consuming Annotator
to activate it.)

2.

Add minimal metadata extraction ability to the PDF plugin

From now on, the Document plugin is not supposed to be loaded,
when using the PDF plugin.

The PDF plugin is now replacing this functionality for PDF.
(Currently, it can only extract URLs and title, but that's all
we have or need for now.)
Add more comments
Simplify url extraction
PDF: Handle documents with null title
Fix PDF URL extraction for FF, again
Stop creating extra quote properties

The canonical (and only) place to find the quote should be the
TextQuoteSelector.
Merge remote-tracking branch 'hypothesis/pdf-update' into typed-packaging
Merge remote-tracking branch 'hypothesis/typed-packaging' into typed-packaging-MSA-2
Revert "Stop creating extra quote properties" - readlift needs the
quotes!

This reverts commit ce90a277c7286139830e3f03eec8a516abcf3391.