refactor engine testing scenario

Engine is now tested standalone by leveraging a dummy rails app
Enable Guard for speedy testing
Move factories to the more standard location `spec/factories/*`
Update README with a Testing section
Rename migrations to contain datetimestamps for their version to fix migration order issues when migrating the dummy application

lib/refinery/blog/engine.rb

@@ -0,0 +1,21 @@
+module Refinery
+  module Blog
+    class Engine < Rails::Engine
+      config.to_prepare do
+        require 'refinery/blog/tabs'
+      end
+
+      initializer "init plugin", :after => :set_routes_reloader do |app|
+        Refinery::Plugin.register do |plugin|
+          plugin.pathname = root
+          plugin.name = "refinerycms_blog"
+          plugin.url = app.routes.url_helpers.refinery_admin_blog_posts_path
+          plugin.menu_match = /^\/refinery\/blog\/?(posts|comments|categories)?/
+          plugin.activity = {
+            :class => Refinery::BlogPost
+          }
+        end
+      end
+    end
+  end
+end