The locked pages configuration is moving to a locked_pages option in the
setup file, and the allowed attachments configuration to
allowed_attachments. The admin prefs page can still be used for these, but
that's depreacted and will only be shown if there's currently a value.
Currently includes UI, and a few tests of the attachment, as well as the
framework to extend pagespecs to test attachments. Does not actually save
the file yet.