Use Holo date/time picker layouts on very small screens

If the screen is smaller than "small" then use the Holo picker layouts.
Unifies the SavedState between delegates so that we can seamlessly
transition between them during configuration changes. Pushes the
DatePickerSpinnerDelegate up to the same level as the calendar delegate.

Bug: 27239893
Change-Id: Ida4dc2748d38bd766ae93d12aef15e963921939c