Media controller specs (#2022)

* Add spec for media controller

* Add MediaAttachment.attached scope

* Simplify methods in media controller

app/models/media_attachment.rb

@@ -33,6 +33,7 @@ class MediaAttachment < ApplicationRecord
 
   validates :account, presence: true
 
+  scope :attached, -> { where.not(status_id: nil) }
   scope :local, -> { where(remote_url: '') }
   default_scope { order('id asc') }