Allow TimePicker/DatePicker to use legacy layout style

In L, the TimePicker was rewritten to use a clock face and the
DatePicker was rewritten to use a calendar. This
change allows developers to opt into the old style instead
(android:timePickerMode="spinner|clock" and
android:datePickerMode="spinner|calendar").)

Issue #16717952 Pre-L style android.widget.TimePicker on L
Issue #16846963 Allow developer to use legacy DatePicker appearance

Change-Id: I4ee071fcbc5bf25eab83d6a5cb6ff352a603f90a