Profile redirect notes (#5746)

* Serialize moved accounts into REST and ActivityPub APIs

* Parse federated moved accounts from ActivityPub

* Add note about moved accounts to public profiles

* Add moved account message to web UI

* Fix code style issues

app/models/account.rb

@@ -42,6 +42,7 @@
 #  followers_url           :string           default(""), not null
 #  protocol                :integer          default("ostatus"), not null
 #  memorial                :boolean          default(FALSE), not null
+#  moved_to_account_id     :integer
 #
 
 class Account < ApplicationRecord
@@ -100,6 +101,9 @@ class Account < ApplicationRecord
   has_many :list_accounts, inverse_of: :account, dependent: :destroy
   has_many :lists, through: :list_accounts
 
+  # Account migrations
+  belongs_to :moved_to_account, class_name: 'Account'
+
   scope :remote, -> { where.not(domain: nil) }
   scope :local, -> { where(domain: nil) }
   scope :without_followers, -> { where(followers_count: 0) }
@@ -133,6 +137,10 @@ class Account < ApplicationRecord
     domain.nil?
   end
 
+  def moved?
+    moved_to_account_id.present?
+  end
+
   def acct
     local? ? username : "#{username}@#{domain}"
   end