Refactoring to move page display code into separate class

Idea is to create reusable PDFViewer that will not have dependency on the PDFView (toolbars, find controller, etc).

- [x] Move pages container logic into PDFViewer (?) out of PDFView
- [x] Move thumbs container logic into PDFThumbnailsViewer (?) out of PDFView
- [ ] Remove all dependency on PDFView in PDFViewer and classes its using
- [ ] Remove any rendering logic from PDFView
- [ ] Isolate PDFPageSource logic and use that in PDFViewer, PDFThumbnailsViewer, PDFFindController

NOTE: The refactoring shall not include any optimization or bug fixes