[ChooseAccount/AccountManager.newChooseAccountIntent Bug Fixes]

Fixing lots of bugs related to the ChooseAccount Activities.
1. Fix jank which is seen when no accounts are present on the device.
2. After addition of the account, return to the user.
3. Don't crash when the user provides null to allowableAccountTypes.
4. Updated documentation of AccountManager#newChooseAccountIntent.
5. Fix NPE.

Bug: 13104800
Bug: 17926560
Bug: 9626001

Change-Id: I0d1913e46560cfb458526a7c930a38049602d8f1