Add tasks for open/close registration (#1823)

* Add tasks for open/close registration

* Code climate style fix

* Use true instead of string 'true'

lib/tasks/mastodon.rake

@@ -82,6 +82,22 @@ namespace :mastodon do
     end
   end
 
+  namespace :settings do
+    desc 'Open registrations on this instance'
+    task open_registrations: :environment do
+      setting = Setting.where(var: 'open_registrations').first
+      setting.value = true
+      setting.save
+    end
+
+    desc 'Close registrations on this instance'
+    task close_registrations: :environment do
+      setting = Setting.where(var: 'open_registrations').first
+      setting.value = false
+      setting.save
+    end
+  end
+
   namespace :maintenance do
     desc 'Update counter caches'
     task update_counter_caches: :environment do