Add override for GdkPixbuf.Pixbuf.new_from_data. Fixes #225

new_from_data isn't bindable (see https://bugzilla.gnome.org/show_bug.cgi?id=721497) and will result in use after free. While we could try to move people away from it and skip it in GI a github code search turns up quite a few users.

This adds an override for it, wrapping GdkPixbuf.Pixbuf.new_from_bytes, and marks any usage of the callback args as deprecated.