Correctly save and restore state.

ManagePermissionsActivity always created a new fragment even when it
had an old one to restore, which meant its fragments could not
properly restore their state (and presumably wasted some resources).

In addition, this also cleans up some of the PermissionUsageFragment
save/restore code now that I can consistently test it.

Fixes: 130719885
Test: Open PermissionUsageFragment, change each of the menu items it
saves, go to home with "Don't keep activities" enabled, restore it,
and see the menu items are properly restored.
Test: Open each fragment launched from ManagePermissionsActivity, go
to home, then restore the fragment, both with and without the "Don't
keep activities" developer option.

Change-Id: Ief1e406bd4072d10a232fa1fd124d68dabc96512