Fixing preferences derived loading

[araujoarthur0]

Context / Background

• Briefly explain the purpose of the PR by providing a summary of the context

This is fixing an issue in the getDerivedPrefsFromLoadedPrefs method on the user-preferences.js file.
The method was evaluating the loaded preferences in regards to the default ones, but ignoring all the changes it did at the end by returning the wrong variable.
This caused issues when changing the number of keys in the default preferences: for instance, the new key for view in the other PR.

What change is being introduced by this PR?

• How did you approach this problem?
• What changes did you make to achieve the goal?
• What are the indirect and direct consequences of the change?

Returning the correct "derived" variable now.

How will this be tested?

• How will you verify whether your changes worked as expected once merged?

All tests ran fine. Adding or removing lines from preferences stops it from being reset to default.

[codecov]

Codecov Report

Merging #249 into master will increase coverage by 0.65%.
The diff coverage is 76.47%.

@@            Coverage Diff             @@
##           master     #249      +/-   ##
==========================================
+ Coverage   46.90%   47.56%   +0.65%     
==========================================
  Files          12       12              
  Lines         985      984       -1     
  Branches      177      177              
==========================================
+ Hits          462      468       +6     
+ Misses        458      451       -7     
  Partials       65       65              

Impacted Files	Coverage Δ
main.js	0.00% <0.00%> (ø)
js/classes/Calendar.js	66.75% <80.00%> (+1.74%)	⬆️
js/user-preferences.js	87.95% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 362f3ca...d128c32. Read the comment docs.

[tupaschoal]

Ah, is this why my preferences never loaded from one start to another? Ship it!

[tupaschoal]

Ah, remember to edit the changelog.txt

[thamara]

I included it on the changelog.txt.