Add more debug output to initial window size calculation

Should help debugging the common problems here.
EogWindow: Use GtkOverlay and GtkRevealer for fullscreen toolbar

Allows removing the previous hack using an overlaid popup window.
Also produces a nice animation when showing/hiding the toolbar and
makes the toolbar not hide the sidebar.
Raise GTK+ dependency for GtkRevealer

GtkRevealer came with GTK+ 3.9.0.