Issue #1647 NUX: Content on create account screen is shifted up after returning from...

... Terms of Service screen.
Issue #1647 
Because we show and hide the navigation bar when we show the TOS Web View, the view returned from self.view is shorter because the navbar animation has not completed.  I changed it to check the height of the screen since we are hiding the nav bar.
Obtaining the height from `[UIScreen mainScreen].bounds` works in portrait orientation but, it doesn't take into account landscape orientation on the iPad, resulting in the view being pushed down. Since the iPad doesn't have the problem with content shifting, maybe use a conditional to check `IS_IPHONE` and only look at `UIScreen` if its true. 

I think checking UIScreen is probably okay here, but just in general I start to get twichy when I see layout code that looks at the screen because the screen's frame varies from device and doesn't reflect orientation. I'd just want to add a comment in the code clarifying why the height was derived from the screen for the benefit of the next person that comes along.