Consistently use underscores for all export formats

[gaurav]

Reported as:

When exporting as a non-naked Nexus, the sequence names look like this: 'BN001447 EI16D251 Nymphalidae Satyrinae Satyrini Acrophtalmia leuce' But when exporting as a naked Nexus, they look like this: BN001447_EI16D251_Nymphalidae_Satyrinae_Satyrini_Acrophtalmia_leuce All export formats should use the format with underscores.