Fix bug caused by ChunkedStream.length not being fixed
Make PageView serve as placeholder rather than using PlaceholderPageView
Render the page the viewer is currently on
Create continuation points while traversing catalog using stack
Change Catalog.traversePages() to perform real DFS
Fix bug with Catalog.traversePages()
Remove old xref optimization that's not needed anymore

Since xref tables/streams support partial parsing
Clean up StreamManager since no longer need to pass params to callbacks
Convert some warns to logs in viewer.js
Fix bug with accessing undefined PDFView.pagesRefMap