Fix for saving unchecked boxes

[mikaelmattsson]

Includes fixes by #862 but in a different way that uses the default argument of Request::get and make the markup the checkbox the same in the create and edit forms.

And also fix unchecking in edit event social.

Error message when saving social settings:

SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'social_show_whatsapp' cannot be null (SQL: update `events` set `social_show_linkedin` = 0, `social_show_email` = 0, `social_show_whatsapp` = ?, `events`.`updated_at` = 2021-05-02 10:39:54 where `id` = 2

[justynpride]

@mikaelmattsson This is great. I hope it gets merged in soon.

[johannac]

Thank you for submitting this @mikaelmattsson !

[robetus]

How is this a fix? I'm still getting the error on 2.4.0 for the social checkboxes. What exactly is the fix please?