Resolve "comment creation api"

Informationen

• API connection for comments implemented
• comment-list feature for participant removed

#145 (closed) related -> comment-list is in the moment in usage for creator and participant, api doesnt support this feature, comment-list for participant have to be saved in local storage

Testing

• check functionality for create-comment and comment-list

(add some fake data for comment-list)

Known Errors

• back-end returns empty array for post method (find)
• back-end returns 403 forbidden error for patch method (as participant and as creator)

Closes #98 (closed)