Distinguish between verified and non-verified IDs

[dennmuel]

This came up during a workshop of orcid-de: Instead of disabling manual input of ORCID IDs the plugin could distinguish between verified and non-verified IDs. The status could be indicated by the presence / absence of the orcid logo. (This is done in other orcid plugins such as for OJS, too.)

Disabling the manual input poses a problem for works that have authors which are not at the same time users of the eprints installation. This seems to be a common case. The verification could be done via e-mail.