Update Comment-Component: use properties where content can only be text

[FabianWilms]

          Understanding - this applies to the `tagline`. I thought about adding icons e.g. to the `title`. 

If we leave this as is, we maybe need to change the comment-component too, to be consistent. Slots like author, date etc. normally only include text too.

Originally posted by @langehm in #56 (comment)