Allow to close feedback

As a visitor, I want to hide the feedback form, due it's screen consumption

AC:

add a close icon
if the form is clicked, it will disappear for the length of this session
alternatively - transform this into a very small overlay

from: Biber Esser reported an issue

Forced Page overlay "please Provide feedback" cannot be closed/Hidden and Covers large Part of the screen

Reported URL:https://my.typo3.org/my-profile/use-typo3-slack?tx_t3oslack_pi1%5Baction%5D=message&tx_t3oslack_pi1%5Bcontroller%5D=SlackUser&cHash=738b2b79debaf46407db6c24a5c27cc8

User Agent:Mozilla/5.0 (Android 9; Mobile; rv:68.0) Gecko/68.0 Firefox/68.0

Edited Nov 11, 2019 by Stefan Busemann