use prefs-style layout for setup wizard date/time settings on non-xlarge screens

Adjusted the screen size test to fall back to phone version of
DateTimeSettingsSetupWizard on large screens.

I made the following changes from how the phone version works:

1. Some layout changes. (Tablet look, bigger margins.)
2. Use zone picker to select time zone.
3. Added isFirstRun boolean extra to hide the pref fields
we don't need to see from setup wizard

Furthermore, I made the following fixes to the existing phone flow
(which had probably never yet been tried on a phone):

1. Added conditionals around access to some variables that only
exist in the xlarge layout.
2. Implemented PreferenceFragment.OnPreferenceStartFragmentCallback
in DateTimeSettingsSetupWizard in order to catch the user tapping
on the timezone preference and show the time zone picker popup.
(Note: for phones in ICS, we might want to launch the zone picker
preferences style, like it would have been had this been a
PreferenceActivity. Or maybe we should just create a separate
DateTimeSettingsSetupWizardPhone activity that subclasses
PreferencesActivity and doesn't need to play this trick.)

Change-Id: Ib5774a005c9f44d730d86c13746d91eb712141cc