Lists (#5703)

* Add structure for lists

* Add list timeline streaming API

* Add list APIs, bind list-account relation to follow relation

* Add API for adding/removing accounts from lists

* Add pagination to lists API

* Add pagination to list accounts API

* Adjust scopes for new APIs

- Creating and modifying lists merely requires "write" scope
- Fetching information about lists merely requires "read" scope

* Add test for wrong user context on list timeline

* Clean up tests

app/models/list.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+# == Schema Information
+#
+# Table name: lists
+#
+#  id         :integer          not null, primary key
+#  account_id :integer
+#  title      :string           default(""), not null
+#  created_at :datetime         not null
+#  updated_at :datetime         not null
+#
+
+class List < ApplicationRecord
+  include Paginable
+
+  belongs_to :account
+
+  has_many :list_accounts, inverse_of: :list, dependent: :destroy
+  has_many :accounts, through: :list_accounts
+
+  validates :title, presence: true
+end