Add UI for setting up account migration (#5832)

config/locales/en.yml

@@ -347,6 +347,8 @@ en:
     invalid_reset_password_token: Password reset token is invalid or expired. Please request a new one.
     login: Log in
     logout: Logout
+    migrate_account: Move to a different account
+    migrate_account_html: If you wish to redirect this account to a different one, you can <a href="%{path}">configure it here</a>.
     register: Sign up
     resend_confirmation: Resend confirmation instructions
     reset_password: Reset password
@@ -454,6 +456,10 @@ en:
     validations:
       images_and_video: Cannot attach a video to a status that already contains images
       too_many: Cannot attach more than 4 files
+  migrations:
+    acct: username@domain of the new account
+    currently_redirecting: 'Your profile is set to redirect to:'
+    proceed: Save
   moderation:
     title: Moderation
   notification_mailer:
@@ -568,6 +574,7 @@ en:
     export: Data export
     followers: Authorized followers
     import: Import
+    migrate: Account migration
     notifications: Notifications
     preferences: Preferences
     settings: Settings

config/navigation.rb

@@ -5,7 +5,7 @@ SimpleNavigation::Configuration.run do |navigation|
     primary.item :web, safe_join([fa_icon('chevron-left fw'), t('settings.back')]), root_url
 
     primary.item :settings, safe_join([fa_icon('cog fw'), t('settings.settings')]), settings_profile_url do |settings|
-      settings.item :profile, safe_join([fa_icon('user fw'), t('settings.edit_profile')]), settings_profile_url
+      settings.item :profile, safe_join([fa_icon('user fw'), t('settings.edit_profile')]), settings_profile_url, highlights_on: %r{/settings/profile|/settings/migration}
       settings.item :preferences, safe_join([fa_icon('sliders fw'), t('settings.preferences')]), settings_preferences_url
       settings.item :notifications, safe_join([fa_icon('bell fw'), t('settings.notifications')]), settings_notifications_url
       settings.item :password, safe_join([fa_icon('lock fw'), t('auth.change_password')]), edit_user_registration_url, highlights_on: %r{/auth/edit|/settings/delete}

config/routes.rb

@@ -96,6 +96,7 @@ Rails.application.routes.draw do
     end
 
     resource :delete, only: [:show, :destroy]
+    resource :migration, only: [:show, :update]
 
     resources :sessions, only: [:destroy]
   end