EvSidebarThumbnails: render thumbnails correctly for hi-dpi displays

Render thumbnails with resolution from gtk_widget_get_scale_factor() and
recreate them when the scale change. Make the thumbnail-rendering helper
functions create a hi-resolution surface when the widget has a scale
factor.

https://bugzilla.gnome.org/show_bug.cgi?id=723431
libview: Fix g_return condition in set_device_scale_on_surface()

Fail when device scale is not 1 if hidpi is not available, we were doing
the opposite.
Remove the  Next-Page and Previous-Page buttons from the toolbar.

Move the actions to the View menu.
Also move the Last Page and First Page to the View menu.

https://bugzilla.gnome.org/show_bug.cgi?id=732289
Remove unused ev_toolbar_create_button and ev_toolbar_create_button_group

https://bugzilla.gnome.org/show_bug.cgi?id=732289
"<Ctrl>Home/End" scroll to the start/end of the document

Before they scroll to the first/last page. This is now managed
by the view, instead of the window.

https://bugzilla.gnome.org/show_bug.cgi?id=724273
libview: Emit accessible focused-changed signals for form fields

https://bugzilla.gnome.org/show_bug.cgi?id=733662