gschem: Add accessors to GschemPageGeometry
gschem: Create pan_general and zoom_extents in GschemPageGeometry
gaf: add missed ChangeLog generation

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Edward Hennessy <ehennes@sbcglobal.net>
gschem: Fix warnings during preview window destruction
gschem: Update grid info when switching pages
gschem: Add lazy evaluation of zoom extents to GschemPageView
gschem: Add callback for GschemPageView signal notify::page