* 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)

ref https://tc39.github.io/proposal-decorators/

* feat: Revocable sessions

* fix: Tests using sign_in

* feat: Configuration entry for the maximum number of session activations

* Introduce domains method to Account relation

Account had followers_domains method, which was excessively specific.
Let relation of Account have domains method instead.

* Move follow_mapping in Account to AccountInteractions

* Introduce shared examples for AccountAvatar inclusion

* Cover Account more

* Fix regression from #3842

Simplify the query by omitting all direct statuses. Private statuses
are allowed because they are from accounts we are following (so
by definition)

Resolves #3887 (alternative)

* Adjust test

(This patch has been merged as bugfix and reverted, but still valuable as
improvement)

Previously, we've attached IntersectionObserver twice for boosted statuses:
wrapper Status and wrapped Status. but wrapped Status don't need to manage
intersection and visibility by itself, because it's a part of wrapper Status.