Allow navigating to the previous/next page using the keyboard's left and
right arrows. I wish this would be the default, and that the themes
would provide more key navigation, but that doesn't seem on the roadmap.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>