posts: eager load uploader and media asset on posts show page.

Eliminate a couple SQL queries by loading the uploader and media asset
in the same query as the post.

app/controllers/posts_controller.rb

@@ -27,7 +27,7 @@ class PostsController < ApplicationController
   end
 
   def show
-    @post = authorize Post.find(params[:id])
+    @post = authorize Post.eager_load(:uploader, :media_asset).find(params[:id])
 
     if request.format.html?
       include_deleted = @post.is_deleted? || (@post.parent_id.present? && @post.parent.is_deleted?) || CurrentUser.user.show_deleted_children?