comments: put search form on same page as search results.

* Remove the /comment/search page. Instead put the comment search form
  on the same page as the search results, so you don't have to go back
  and forth to update your search.
* Add an "Edited?" search option, for finding comments that have been edited.
* Add options for sorting by oldest comments and lowest scoring comments.

config/routes.rb

@@ -85,7 +85,7 @@ Rails.application.routes.draw do
       get "/", action: :index
     end
     collection do
-      get :search
+      get :search, to: redirect("/comments?group_by=comment")
     end
     member do
       post :undelete