[#2684] Remove/replace display_name (roepnaam)

[jiromaykin]

Taiga:
https://taiga.maykinmedia.nl/project/open-inwoner/task/2684

See also previous issue:
#1270

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.20%. Comparing base (a430792) to head (013fe47).
Report is 21 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1362      +/-   ##
===========================================
+ Coverage    95.19%   95.20%   +0.01%     
===========================================
  Files         1002     1005       +3     
  Lines        37029    37169     +140     
===========================================
+ Hits         35248    35388     +140     
  Misses        1781     1781              

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[jiromaykin]

@pi-sigma This was much more back-end than I expected, so hopefully I didn't remove too much from the tests...
I'm mostly replacing display_name with first_name,
but we also used to have have a short_name here and there, so not sure if we should bring that back again to revert the change from #1270 .

[pi-sigma]

"return a or a" is redundant. Context: I introduced call_name to show either the display_name or the first_name, in case the display_name was not set. Now that we're getting rid of the model field display_name, I suggest renaming the propery to "display_name" and return the first name for now. If some municipalities decide they want to display user names in a different way, we can easily customize it:

@property
def display_name(self)
    return self.first_name

You'll need to change it in profile/me.html as well

[jiromaykin]

@pi-sigma Ah yes, but I removed the Display name field from there completely, since it already has a separate field for first name. Or does this mean we need to use display_name everywhere instead of the first_name? Like in me.html, mydata.html and edit.html?

[jiromaykin]

@pi-sigma I think this looks good now, thanks 😊