Revert "Hide usage graph on app usage details pages."

This reverts commit 1740ce4f.

The data usage graph is useful information to show for a single app as
well (as it shows the app's share of data usage compared to the total).
Additionally, this commit broke navigation back from data usage when
entering it from an app's details pane.

Change-Id: Ia1de61d24aebfef3537e4d2c358e63b12a588838