Fix filter bug for non-internal app filtering.

By default, the filter would show all non-categorized apps. This,
however, regressed the external storage apps view which does not have
categorization (yet). By adding back in a legacy option to use the old
purely UUID filtering, we can fix the regression.

Change-Id: I72d8d3bc08fbdff53374eb1e973bce9f8d7e2e79
Fixes: 63542896
Test: Settings unit test