Refresh email notifications (part I)

* Use strings that fit properly in new notifications
* General cleanups & rewrites from Roy
* Remove showWarningNotification() and use postAccountNotification()

This is part I.  Part II will add dialogs triggered by some of these
notifications, to provide more explanation to the user of what's wrong
and how to fix it.

Bug: 3238657
Change-Id: Ib51bcb4412f8a09a6f97653f0b5f8642efe2ac1e
3 files changed