"… can specify that an image pane should show an entire image" runtime.

starts: [#68397404] (runtime changes only here)

"An author can specify that an image pane should show an entire image.
When the activity is run, add scaled borders around the image as
needed so that the whole image is always seen."

https://www.pivotaltracker.com/story/show/68397404
Bottom navigation UI shows current page, but doesn't imply navigation.

[#72097370]

https://www.pivotaltracker.com/story/show/72097370
Remove "Back" button.  [#72097370]

https://www.pivotaltracker.com/story/show/72097370