Allow parallel responding to comments

[georgimld]

(Similar to issue #46)

This should be possible:

• initial state: have one post with 2 separate comments on it: (e.g. on the news feed page):

• click respond on one of the comments and type something
• click respond on the other comment and tye something (in paralell to the one above)
• finish one of the responses and submit it

At the moment this is not possible and when clicking on another respond button while already editing another response, the "verwerfen" and "senden" buttons flicker and no new input field is open