Fix conflict between normalize and array_attribute macros.

Fix the `normalize` and `array_attribute` macros conflicting with each
other on the WikiPage model. This meant code like
`wiki_page.other_names = "foo bar"` didn't work. Both macros defined a
`other_names=` method, but one method overrode the other.

The fix is to use anonymous modules and prepend so we can chain method
calls with super.

app/models/wiki_page.rb

@@ -10,12 +10,13 @@ class WikiPage < ApplicationRecord
   normalize :body, :normalize_text
   normalize :other_names, :normalize_other_names
 
+  array_attribute :other_names # XXX must come after `normalize :other_names`
+
   validates :title, tag_name: true, presence: true, uniqueness: true, if: :title_changed?
   validates :body, presence: true, unless: -> { is_deleted? || other_names.present? }
   validate :validate_rename
   validate :validate_other_names
 
-  array_attribute :other_names
   has_one :tag, :foreign_key => "name", :primary_key => "title"
   has_one :artist, -> { active }, foreign_key: "name", primary_key: "title"
   has_many :versions, -> {order("wiki_page_versions.id ASC")}, :class_name => "WikiPageVersion", :dependent => :destroy