Remove unused popup menus

Removed in the port to WebKit2

https://bugzilla.gnome.org/show_bug.cgi?id=690062
Cleanup context menus

https://bugzilla.gnome.org/show_bug.cgi?id=690062
Use the suggested filename when saving images

https://bugzilla.gnome.org/show_bug.cgi?id=572819
Add an about: handler

https://bugzilla.gnome.org/show_bug.cgi?id=665484
Improve oops screens

https://bugzilla.gnome.org/show_bug.cgi?id=692336