Fix touch ripples for setup wizard screens

Make PreferenceTheme.SetupWizard inherit from PreferenceTheme so the
preference layout from the support library is used.

Automated tests were not added because when trying to test
SettingsActivity under Robolectric, it fails due to the lack of API
24 support.
(https://github.com/robolectric/robolectric/issues/2554)

Test: (Manual) Ripples shown when touched and keyboard focused.
Bug: 32671413
Change-Id: I5271aaddbcfdb7ee0a71bc3c223e6dc62a5ecb47