With the new propgui UI, the property nick is used as the combo's
label; since the descriptions of the corresponding enum values are
quite long, using "deficiency" as a label for the prop is
problematics, especially for some translations.

Change the property name and nick to "type", and align the code
with the change.

Also, change the property's blurb from "color deficiency type" to
"color vision deficiency type".