IssueTracker

Before you start, please check existing proposals at https://issuetracker.google.com/issues?q=hotlistid:3426315%20status:open

Description:
Add the ability to `navController.navigateForward()` or `navController.navigateDown()` as opposite to `navController.navigateUp()`

Use Case:
This makes the user more confident when navigating in the application since they can navigate back and forward
very freely.  Its gives the browser experience right in the application.

Currently, we use our custom lightweight (bug prone) navigation mechanism just to provide this feature.