change to idiomatic use of layouts versus regular views

no functional change here, but familiar Rails users will see view files in the
locations they expect. this also slightly simplifies controller code

there is one attendant change in the wiki at `rails_3/A1-SQL-Injection-Interpolation.md`
that I'm happy to make after the PR is merged.

app/controllers/dashboard_controller.rb

@@ -15,12 +15,12 @@ class DashboardController < ApplicationController
   end
 
   def bar_graph
-    render :partial => "layouts/dashboard/bar_graph"
+    render :bar_graph, layout: false
   end
 
   def pie_charts
      @user = current_user
-     render :partial => "layouts/dashboard/dashboard_stats"
+     render :dashboard_stats, layout: false
   end
 
 end