Create setup flow for use by Accounts manager.

* 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.
1 file changed