Check for curly braces for author's surname

[magsilva]

Some digital libraries export citation where author's surname a field is wrapped with curly braces. Although this avoids incorrect changes of letter's case when using the entry as reference in a LaTeX document, it breaks completely valid formatting. I would say this is an incorrect hack/workaround for such issue. Thus, JabRef could deploy some verification for extra curly braces for author's surname.