Handle improperly formatted dates from Symplectic Elements on import

[hakbailey]

Trying to import a paper that has an unexpected date format will result in a system error presented to the user. Instead, we should present a message to the user that the date format needs to be fixed in Symplectic Elements for that paper, and continue processing paper imports for the current author. See author ID 12938 for an example of an improper date format that will cause this error.