* Fix #4058 - Use a long-lived cookie to keep track of user-level sessions

* Fix tests, smooth migrate from previous session-based identifier

* Add overview of active sessions

* Better display of browser/platform name

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

* Fix test

* feat: Revocable sessions

* fix: Tests using sign_in

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

* Dont use raise_error by itself (avoids warning)

* Add coverage for AccountFilter

* Improve coverage and refactor for Subscription#lease_seconds

* Improve coverage and refactor for NotificationMailer

* Simplify assignment of min/max threshold on subscription

* Make private toots get PuSHed to subscription URLs that belong to domains where you have approved followers

* Authorized followers controller, stub for bulk action

* Soft block in the background

* Add simple test for new controller

* Rename Settings::FollowersController to Settings::FollowerDomainsController, paginate results,
rename "private" post setting to "followers-only", fix pagination style, improve post privacy
preferences style, improve warning style

* Extract compose form warnings into own container, show warning when posting to followers-only with unlocked account

Devise changed their approach -
3f3ec236bb

This change silences a deprecation warning about `TestHelpers`

This commit introduces Capybara and the first feature spec.

I focused on coverage for log in for the first feature spec because that would
have prevented 624a9a7136 causing #1236.

behaviour with Turbolinks enabled, optimizing Rabl for production