Add collaborative legislation summary again

It was removed in commit 128a8164 because we hadn't reviewed it nor
tested it properly. We're now adding it again, fixing the issues we've
found while reviewing.

app/models/legislation/draft_version.rb

@@ -40,4 +40,8 @@ class Legislation::DraftVersion < ApplicationRecord
   def total_comments
     annotations.sum(:comments_count)
   end
+
+  def best_comments
+    Comment.where(commentable: annotations, ancestry: nil).sort_by_supports.limit(10)
+  end
 end