:bug: Reactivity issue on MucCommentText

[langehm]

Describe the bug
Changes on the prop date will not be propagated.

To Reproduce
Steps to reproduce the behavior:

1. Go to MucCommentText
2. Take the default example with empty date to begin with
3. Enter some string
4. ... wait forever because nothing will change

Expected behavior
The newly entered date should be displayed in combination with a dateprefix.

Screenshots

Additional context
Add any other context about the problem here.