* feat(components/media_gallery): Responsive images

* fix(components/media_gallery): Link to image URL

This also resolves the issues where sometimes the timestamps wrap and also sits unpleasantly close to the … button.

* Fix #3910 - Require OTP authentication to disable 2FA. Also, remove ability
to generate new OTP backup codes *after* initial backup codes were handed
out during activation

* Restore recovery code re-generation

* Improve display of some 2FA elements

* Add overview of active sessions

* Better display of browser/platform name

* Improve how browser information is stored and displayed for sessions overview

* Fix test

* Remove unused column_collapsable.js
* Remove old styles
* Extract `> div`  style to independent class

Avatars now have consistent styling across all pages; border radius can be adjusted with a SASS variable ($ui-avatar-border-size)

* Replace TextIconButton for SensitiveButton to IconButton

* line-height

* Add form for account deletion

* If avatar or header are gone from source, remove them

* Add option to have SuspendAccountService remove user record, add tests

* Exclude suspended accounts from search

* Unread indicator was invisible behind column header, adjusted

* Unread indicator now a CSS pseudo-element

* Adjust flex

* Re-add clear notifications button

* remove connect() in column_settings

* one line

* remove unused props