clean up stuff

[yeldiRium]

I used Intellijs code inspection feature and cleaned up most of the ESLint errors and some other issues. I also probably fixed some minor bugs along the way. Also we now don't have the populate* functions anymore, since they weren't used and broken anyway.

Please review carefully because of the many small and unrelated changes.

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This change is 

[codecov[bot]]

Codecov Report

Merging #74 into develop will increase coverage by 0.01%. The diff coverage is 0%.

@@            Coverage Diff             @@
##           develop     #74      +/-   ##
==========================================
+ Coverage      0.2%   0.22%   +0.01%     
==========================================
  Files           56      56              
  Lines         1438    1360      -78     
  Branches       127     111      -16     
==========================================
  Hits             3       3              
+ Misses        1308    1246      -62     
+ Partials       127     111      -16

Impacted Files	Coverage Δ
frontend/src/model/OwnedResource.js	0% <ø> (ø)	:arrow_up:
frontend/src/api/Util/Parse.js	0% <ø> (ø)	:arrow_up:
frontend/src/store/modules/Questionnaires.js	0% <ø> (ø)	:arrow_up:
frontend/src/model/SurveyBase/Question.js	0% <ø> (ø)	:arrow_up:
frontend/src/api/Util/Response.js	17.64% <ø> (ø)	:arrow_up:
frontend/src/store/modules/Dimensions.js	0% <ø> (ø)	:arrow_up:
frontend/src/Plugins/HandleApiError/index.js	0% <ø> (ø)	:arrow_up:
frontend/src/Plugins/LoadingSpinnerModal/index.js	0% <ø> (ø)	:arrow_up:
frontend/src/store/index.js	0% <ø> (ø)	:arrow_up:
frontend/src/store/modules/Statistics.js	0% <ø> (ø)	:arrow_up:
... and 16 more

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