Version 1.3.0
* Target Android 8.1 (Oreo); dropped support
  for Android 2.2 (Froyo) through 3 (Honeycomb).
* Major changes (internal and external) to the alarm notification system:
  * When running on Oreo or higher, vibrate and alarm
    sound settings are removed from the app Settings page;
    these are instead managed by the Android system.
  * When creating or updating a To Do item with an alarm enabled,
    check whether permission has been given to post notifications.
    If not, alert the user to enable this in the system settings.
  * Instead of putting the text of all To Do alarms in the same
    notification, the app creates a separate notification for each
    due (or overdue) item.  When the user clicks on a notification,
    the app switches to the category for that item if needed.
  * Notifications are no longer automatically cleared when clicked.
    Instead, completing a To Do item clears any associated notification.
