title: Why I can't add left bar button item to Navigation Item through Interface Builder?
body: <p>It only allows me to add the right barbutton, but when I drag another barbuttonitem, it's simply denied.
  I looked at the properties of NavigationItem, and I saw that there are outlets for right barbutton and even for the back barbutton. 
  So: why can't I add a left barbutton item to the Navigation Item (through Interface Builder)?</p>