Back button always closes the hierarchy view

#### Software and hardware versions
All versions

#### Problem description
Back button always closes the hierarchy view

If a user navigates through groups/questions it's confusing that clicking on the back button causes returning to `FormEntryActivity` instead of going back to the previous level of the hierarchy.

Start by tracing back-button handling for the hierarchy view and how it returns to FormEntryActivity. Reproduce navigation through groups and questions, then verify that Back returns to the previous hierarchy level rather than closing the view.

Written by the indexing model from the issue text.