Show warnings when skipping Wi-Fi connection

If user skips over Wi-Fi, warn about possible carrier data charges or
inability to receive updates, depending on whether or not phone
service is available.

Note to translators: Some strings are being moved here from setup
wizard. They're tagged with their msgid's so as not to trigger
retranslation.

Bug: 7211786
Change-Id: Idec7863377bd453d1808b26ee3da75f8310b32e0