Added frontend functionality to display 'today' or 'tomorrow' in the event header instead of date

Closes #1120 (closed)

What does this MR do?

Replaces the date in the event header with 'today' (or 'tomorrow) if the event takes place today or tomorrow.

How confident are you it won't break things if deployed?

Should be fine :) however feedback is appreciated!

Links to related issues

How to test

1. Checkout branch locally
2. Login as userbot@example.com
3. Create new appointment (from dashboard go to 'Deine Bezirke, Göttingen' -> on the left side click 'Termine' -> on the right side 'Neuen Termin eintragen' -> fill the form and save)
4. Go back to dashboard. The event header shows 'Heute' if appointment's date is today (or 'Morgen' accordingly).

Screenshots (if applicable)

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• used "state:" labels to track this MR's state until it was beta tested
• added an entry to CHANGELOG.md
• added a short text that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in the Beta Testing forum: https://foodsharing.de/?page=bezirk&bid=734&sub=forum
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...) how this change can be tested.
  • Be aware, that also non technical people should understand.

Release notes text in German