_element_type not filled in for PersonNameElement

It seems like you can specify the alias for an identity using the CIQ stuff.

``` xml
<xnl:PersonName xnl:Type="Alias">
     <xnl:NameElement>Rodney</xnl:NameElement>
</xnl:PersonName>
```

This information doesn't seem to be captured.  It would be helpful for the elevator in order to fill in the alias property of certain STIX 2.1 objects.