shell: Check "page-changed" in EvSidebarBookmarks

Currently, a second click of a previously selected bookmark always
begins renaming the bookmark, even after one has navigated away from
the bookmark. The listener unselects the bookmark as soon as one moves
to a different page, allowing one to easily jump back to the bookmark.

Fixes #623.
5 jobs for toc-navigation in 28 minutes and 43 seconds (queued for 38 seconds)
Status Job ID Name Coverage
  Build
passed #777625
flatpak
flatpak

00:20:58

manual #777614
allowed to fail manual
master
passed #777615
meson

00:13:56

manual #777616
allowed to fail manual
meson-gtk-doc
failed #777617
flatpak
flatpak

00:04:41