Svenska Ärenden custom features for Oodikone

[tttriple]

https://www.helsinki.fi/sv/om-oss/det-har-ar-helsingfors-universitet/det-tvasprakiga-universitet

Svenska Ärenden would benefit ("needs") custom population /data from two groups of students:

#1 (those in) TVEX
#2 citizenship: swedish

We already have filter for #2 (in population view) but need to add custom feature to build a population of all the students that have that particular citizenship.

(NOTE: how to handle dual nationality?) Students with multiple citizenships are now handled correctly, citizenships are always stored as a list

TVEX can be found in sisu, please see the attached picture. Custom population and filter of TVEX students is needed too.