added legacy api for posts

app/controllers/legacy_controller.rb

@@ -0,0 +1,11 @@
+class LegacyController < ApplicationController
+  def posts
+    @post_set = PostSets::Post.new(tag_query, params[:page])
+    @posts = @post_set.posts
+  end
+
+private
+  def tag_query
+    params[:tags] || (params[:post] && params[:post][:tags])
+  end
+end