Fix the sweep and dihedral chord percantage spinbox for wing elements

[svengoldberg]

This PR fixes the wrong behaviour of the spinboxes that adjust the wing sweep and dihedral chord percantages.
Here, default values were set hard-wired that overwrote the user selection.
Moreover, during the internal update, the sweep computation used the wrong spinbox value.

Fix #1221.

Description

How Has This Been Tested?

Screenshots, that help to understand the changes(if applicable):

Checklist:

Task	Finished	Reviewer Approved
At least one test for the new functionality was added.	yes does not apply	OK
New classes have been added to the Python interface.	yes does not apply	OK
The code is properly documented with doxygen docstrings	yes does not apply	OK
Changes are documented at the top of ChangeLog.md	yes does not apply	OK

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.96%. Comparing base (8350f01) to head (eb48c2f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1327   +/-   ##
=======================================
  Coverage   72.96%   72.96%           
=======================================
  Files         322      322           
  Lines       28290    28290           
=======================================
  Hits        20643    20643           
  Misses       7647     7647           

Flag	Coverage Δ
unittests	72.96% <ø> (ø)

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[joergbrech]

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