GCS: confirm failsafe is working during input wizard

Some receivers have a failsafe mode that do things like hold
the throttle at a constant setting. In this situation, the flight
controller cannot tell that the pilot is no longer in control.
    
This is an extremely unsafe configuration and should not be
facilitated by the wizard. This adds a step that requires the
user to verify that failsafe detection is working reliably.

This also makes a few cosmetic improvements to the wizard so 
it looks like this:
![screen shot 2014-09-06 at 8 50 14 pm](https://cloud.githubusercontent.com/assets/618346/4177281/91252c16-3631-11e4-88b4-9cc2311435d6.png)

How does that allow this? I just had one situation where the welcome screen next button was grayed out (I guess I cancelled at the wrong time). This makes sure next is available when you start (as it normally is).