Bind web UI access tokens to sessions (#3940)

* Add overview of active sessions

* Better display of browser/platform name

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

* Fix test

* Fix #2347 - Bind web UI access token to session

When you logout, session also destroys the access token, so it's no longer
valid. If access token is destroyed some other way, the session is also
destroyed, requiring a re-login.

Fix #1681 - Add scheduler to remove revoked access tokens and grants

* Fix test

app/controllers/application_controller.rb

@@ -11,6 +11,7 @@ class ApplicationController < ActionController::Base
   include UserTrackingConcern
 
   helper_method :current_account
+  helper_method :current_session
   helper_method :single_user_mode?
 
   rescue_from ActionController::RoutingError, with: :not_found
@@ -68,6 +69,10 @@ class ApplicationController < ActionController::Base
     @current_account ||= current_user.try(:account)
   end
 
+  def current_session
+    @current_session ||= SessionActivation.find_by(session_id: session['auth_id'])
+  end
+
   def cache_collection(raw, klass)
     return raw unless klass.respond_to?(:with_includes)