New look for event header panels and dashboard invitations

What does this MR do?

Rebuilds the event header panels in Vue, adds some features and better layout.

Check each commit for details ;-)

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

Right now this would cause some Sentry issues due to the quick&dirty fake-API call. Those should be tackled.
Otherwise it will be okay I guess?

Links to related issues

• waits for !1758 (closed)
• is part of &32
• should be part of &9 (TODO)
• closes #992 (closed)
• https://foodsharing.de/?page=bezirk&bid=2296&sub=forum&tid=115660 Product team

How to test

• create some events in a region
• view them on your dashboard
• view them on their detail page
• check if the links work (edit, change status)
• check if the tooltips work

Screenshots

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
• use "state:" labels to track this MR's state until it was beta tested
• added an entry to CHANGELOG.md
• add 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 Beta Testing Repo

Release notes text

(A short text that will appear in the release notes and describes the change for non-technical people. Not always necessary, e.g. not for refactoring.)