Bug 1109641 - Disable the back/forward buttons when there is nothing to do 

Taking a stab at how communication between the Browser and the Toolbar might work. All I'm doing now is changing enabled/disabled status of the back/forward buttons, but this obviously sets up for displaying load status, stop/reload button, etc...

No hard feelings if rejected, but would love some feedback on the approach! Cheers.
Please remove all trailing whitespace (here and throughout).