Add ability to use nested only parameter

- The only string works much the same as before with its comma separation
-- Nested includes are indicated with square brackets "[ ]"
-- The nested include is the value immediately preceding the square brackets
-- The only string is the comma separated string inside those brackets
- Default includes are split between format types when necessary
-- This prevents unnecessary includes from being added on page load
- Available includes are those items which are allowed to be accessible to the user
-- Some aren't because they are sensitive, such as the creator of a flag
-- Some aren't because the number of associated items is too large
- The amount of times the same model can be included to prevent recursions
-- One exception is the root model may include the same model once
--- e.g. the user model can include the inviter which is also the user model
-- Another exception is if the include is a has_many association
--- e.g. artist urls can include the artist, and then artist urls again

app/models/dtext_link.rb

@@ -8,6 +8,10 @@ class DtextLink < ApplicationRecord
   scope :wiki_page, -> { where(model_type: "WikiPage") }
   scope :forum_post, -> { where(model_type: "ForumPost") }
 
+  def self.model_types
+    %w[WikiPage ForumPost]
+  end
+
   def self.new_from_dtext(dtext)
     links = []
 
@@ -71,4 +75,8 @@ class DtextLink < ApplicationRecord
     # because it can't index values that take up more than 1/3 of an 8kb page.
     self.link_target = self.link_target.truncate(2048, omission: "")
   end
+
+  def self.available_includes
+    [:model]
+  end
 end