Adapt to support PDF.js v1.0.907

... as per #86.

Tested with:
 * Iceweasel 31.2.0 (Shipped with Debian, built on top of Firefox ESR) - ships with PDF.js v1.0.68
 * Firefox 31.3.0 (current ESR a.k.a. Extended Support Release) - ships with PDF.js v1.0.68
 * Firefox 34.0.5 (current stable) - ships with PDF.js v1.0.712
 * Firefox 34.0.5 (current beta - yes, it's the same as stable, just released) - ships with PDF.js v1.0.712
 * Firefox 35.0a2 (developer edition a.k.a. aurora a.k.a. alpha) - ships with PDF.js v1.0.907

According to tests, all involved PDF.js versions are now fully supported.

Some of the fields that used to live under PDFView have now migrated under
PDFViewerApplication. The other half of the fields migrated under
PDFViewerApplication.pdfViewer.

There only way to consistently find them (without changing the client code
on a per-field basis) is to look at both places.

I don't want to change the client code, because in earlier versions, the
fields are under the same object.