Resolve "comment creation - participant component logic"

Information

• edited comment service (get comment function http, delete comment)
• added logic components to comment (get roomId, get comments, back button function)
• added routing
• comment and create-comment style are revised
• edited comment and create-comment, user story #63 (closed) & #5 (closed) should be now finished

Testing

• check code quality
• check functionality
• checkout page http://localhost:4200/room/:roomId/comments by clicking through application -> only creators should have access, check if there are the right comments (compare with db) visible
• login as participant, create a new comment -> login as creator, check if you can see the comment
• check delete function for comment

Closes #51 (closed) Closes #45 (closed)