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/controllers/artists_controller.rb

@@ -31,10 +31,7 @@ class ArtistsController < ApplicationController
     # XXX
     params[:search][:name] = params.delete(:name) if params[:name]
 
-    @artists = Artist.includes(:urls).paginated_search(params)
-    @artists = @artists.includes(:tag) if request.format.html?
-    @artists = @artists.includes(:urls) if !request.format.html?
-
+    @artists = Artist.paginated_search(params).includes(model_includes(params))
     respond_with(@artists)
   end
 
@@ -81,6 +78,14 @@ class ArtistsController < ApplicationController
 
   private
 
+  def default_includes(params)
+    if ["json", "xml"].include?(params[:format])
+      [:urls]
+    else
+      [:urls, :tag]
+    end
+  end
+
   def item_matches_params(artist)
     if params[:search][:any_name_or_url_matches]
       artist.name == Artist.normalize_name(params[:search][:any_name_or_url_matches])