Allow editors to load article authors as frozen records

[mauromsl]

When loading an article via this plugin, editors may want to add author metadata not linked to an account.
It is also possible they may want to set the same address (generic institutional address) as the contact email for multiple frozen author records.

• Author metadata to be stored as Frozen Author

• Author metadata link to account only if an email address is matched with an account

• Checkbox allowing the editor to issue an account for the author if one is not found