Implement Autodiscover for Exchange servers

* Autodiscover allows complete configuration using only email address
  and password
* Code handles the two standard autodiscover addresses and redirect
* Autodiscover process starts when the user chooses "Exchange" as the
  account type.  If the account is created via the AccountManager,
  autodiscover begins upon tapping "Next" for the first time
* If autodiscover fails due to anything other than auth failure for
  autodiscover-capable servers, the user is placed into the standard manual
  configuration screen

Bug: 2366019
Change-Id: I936712b924833d9a133e8da04e11c3ba45d92f92
4 files changed