Fix global events not fired bug
Fix global events not fired bug

The reason that we have to specify a new eventbus is the default behavior
of pdfjs viewers. If you don't specify an eventbus at creation, a viewer will
get a singleton instance of a global eventbus. Meaning that two viewer instances
(in our case PDFSinglePageViewer and PDFViewer) share one eventbus.
Since PDFSinglePageViewer reacts to 'pagesinit' events by calling
'_ensurePageViewVisible()' (see pdfjs source code) the single viewer throws
an error.
Using an unmodified new EventBus instance however resulted in important events
not being thrown at document level (f.e. 'pagerendered'). By copying the
implementation of a global EventBus from 'pdf.js/web/dom_events.js', the normal
behavior is restored with separat EventBus instances.

VadimDez/ng2-pdf-viewer,VadimDez/ng2-pdf-viewer,VadimDez/ng2-pdf-viewer