refactor: add and use parseDate

[vil02]

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Describe your change:

As promissed, this PR adds a function parseDate.

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• All new JavaScript files are placed inside an existing directory.
• All filenames should use the UpperCamelCase (PascalCase) style. There should be no spaces in filenames.
  Example:UserProfile.js is allowed but userprofile.js,Userprofile.js,user-Profile.js,userProfile.js are not
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.07%. Comparing base (bd34e9f) to head (efeab6e).

Additional details and impacted files

@@ Coverage Diff @@ ## master #1643 +/- ## ======================================= Coverage 84.07% 84.07% ======================================= Files 375 376 +1 Lines 19688 19694 +6 Branches 2913 2907 -6 ======================================= + Hits 16552 16558 +6  Misses 3136 3136 

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[appgurueu]

Makes sense.

(Though probably these date-related functions should take "date" objects instead of strings in the first place to save them the (not very interesting) parsing.)