Move graph module from lib or vendor directory to app directory.

Because not autoloading lib directory at development mode.

app/controllers/graph_controller.rb

@@ -20,7 +20,7 @@ class GraphController < ProjectResourceController
     respond_to do |format|
       format.html
       format.json do
-        graph = Gitlab::Graph::JsonBuilder.new(project, @ref, @commit)
+        graph = Graph::JsonBuilder.new(project, @ref, @commit)
         render :json => graph.to_json
       end
     end

app/controllers/projects_controller.rb

@@ -1,5 +1,3 @@
-require Rails.root.join('lib', 'gitlab', 'graph', 'json_builder')
-
 class ProjectsController < ProjectResourceController
   skip_before_filter :project, only: [:new, :create]
   skip_before_filter :repository, only: [:new, :create]