Navigation Bar 

Navigation bar implementation wired in. Interacts properly with the progress bar now so that it can be enabled/disabled and takes the place of the progress bar when enabled.
details.requiredOnScreen == details.answeredOnScreen || details.requiredOnScreen < 1

This looks like it's intended as "all required questions on this screen are answered" but it will also be true if, say, a screen has 2 required, 2 non-required, and user has answered the non-required ones. Is that on purpose?