Separate notifications preferences from general preferences (#4447)

* Separate notifications preferences from general preferences

* Refine settings/notifications/show

* remove preferences.notifications

app/controllers/settings/notifications_controller.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+class Settings::NotificationsController < ApplicationController
+  layout 'admin'
+
+  before_action :authenticate_user!
+
+  def show; end
+
+  def update
+    user_settings.update(user_settings_params.to_h)
+
+    if current_user.save
+      redirect_to settings_notifications_path, notice: I18n.t('generic.changes_saved_msg')
+    else
+      render :show
+    end
+  end
+
+  private
+
+  def user_settings
+    UserSettingsDecorator.new(current_user)
+  end
+
+  def user_settings_params
+    params.require(:user).permit(
+      notification_emails: %i(follow follow_request reblog favourite mention digest),
+      interactions: %i(must_be_follower must_be_following)
+    )
+  end
+end