Implement new calendar

[Process-ing]

Closes #1275

Review checklist

• [X] Terms and conditions reflect the current change
• [ ] Contains enough appropriate tests
• [X] If aimed at production, writes a new summary in whatsnew/whatsnew-pt-PT
• [X] Properly adds an entry in changelog.md with the change
• [X] If PR includes UI updates/additions, its description has screenshots
• [X] Behavior is as expected
• [X] Clean, well-structured code

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 11%. Comparing base (1da2fbf) to head (d5b9f16). Report is 1 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1372 +/- ## ======================================== - Coverage 12% 11% -0% ======================================== Files 265 266 +1 Lines 7209 7340 +131 ======================================== Hits 806 806 - Misses 6403 6534 +131 ```