Back button missing in several pages in latest rc-proposed images

[Nekhelesh Ramananthan]

Since the upstream bug fix for https://bugs.launchpad.net/ubuntu/+source/ubuntu-ui-toolkit/+bug/1565811, several pages in uNav don't show a back button! This forces the user to restart the app to get out of that page. It turns out this issue started with a recent rc-proposed image (somewhere from 17-18 april 2016).

The reason is that in uNav, our pagestack is structured in such a way that it has a page depth of 1. Unfortunately the SDK devs hide the back button at that depth..which is causing this bug. The solution forward would be to talk to sdk devs and patch it in our app with custom back buttons.