They renamed PDFView to PDFViewerApplication, which we need to account
for in our pdfjs scripts.
Also, it seems like the actual viewer is now only created when the DOM
has been loaded. This means that at the time when our script is
executed, the viewer does not yet exist. Thus we need to delay the open
request too by registering a DOMContentLoaded handler.
webelem.javascript_escape got renamed to javascript.string_escape, and a
new javascript.assemble got added to make it easier to call a function
inside a .js file.
Otherwise the stacktrace might be confusing since it will show the
FileNotFoundException as the causing error, which is not true (it just
happens to be the last checked place).
The .path attribute was added so that we still have the requested path
in the error log.
See #1280.
* No modified pdfjs installation needed
-> Groundwork for using a system-wide installation
* Script update_3rdparty.py to download and upack the latest pdfjs
release