Improve PDF/DJVU navigation

When a user clicks the next/previous page buttons, use
history.pushState (if available) to add a new history
item so that the back/forwards browser buttons navigate
the PDF. When a new page of the file is browsed to, also
fire the wikipage.content hook, since the page contents
have changed.

Co-authored-by: Theopolisme <theopolismewiki@gmail.com>
Co-authored-by: Tholam <t.lam@lamsinfosystem.com>
Bug: 55893
Change-Id: Id796bd641612706f7bd04c974065f05f72f2a8e4
Merge "Improve PDF/DJVU navigation"