Fix: Multiple menu item added

Multiple menu items are getting added to the menu, when you add a trailing space to the post name during editing. 

Steps to recrate.
1.) Create a post. 
2.) Edit the post, add a trailing space to the title.
3.) Save it. 
4.) The a new menu item will be added. 
5.) everytime you edit a new item will be added.
moved nav menu code to menu handler class
--- Pushed to GIthub
add code for menu item repeating bug
--- modified further
Merge pull request #3 from codbox/master

Changed the hook from sav_post to transition_post_status