Comment 2 for bug 133074

Patch is the right idea, but needs a couple of changes:
 - DOI isn't the only way to get metadata, there's also eprint, which is considered an "extra field". So sensitivity also needs updating on adding, removing or editing an extra field, and the update needs to check whether the eprint field is present.
 - In update(), canWebLink should be canGetMetadata

Cheers,
John