* Create a new entry point for the exchange setup flow and switch
EASAuthenticatorService to call it
* Pass "eas flow mode" down through the setup screens
* Slightly modify their behavior as we go (e.g. we skip the
(account type" screen since we know it's EAS.)
* Add a checkbox to "sync contacts from this account" and pass that
value into ExchangeStore when we set up the account.
* Change the flow exit to pop back to the account manager instead of
taking the user to the new inbox.
This CL satisfies cases 1 & 2 of bug # 1974752.
