Do not use PDFJS.webViewerLoad to open pdf files

[moesjarraf]

We added a PDFJS.webViewerLoad function so we can decide when the pdf viewer should be initialized, and to open new files, but this is not the way to go. That function is meant to initialize the pdfviewer once and only once.

Instead we should remove that patch and just use PDFViewerApplication.open(file) as stated in the FAQ, to open different files. That function allows a string or an array of bytes as parameter.

So the webviewer should just be initialized on dom load. However, to prevent the pdfviewer from loading an initial file see #3