Tell administrators about a location without a schedule

A notification when a schedule is turned off, then a reminder: once a week while another
location is backed up, every day when none is. The round trip now also checks the text of
these notifications and of the one about names, and that one location never gets two runs.

CHANGELOG.md

@@ -28,6 +28,8 @@ shown under 1.0.0. The git tag of a release candidate goes after the date.
   point has the time its backup really began, not the time it was queued.
 - Choosing a time no longer starts a backup right away when that time has already passed today.
 - A location without a schedule no longer gets the notification that it has had no recent backup.
+  Instead, all administrators are told when a schedule is turned off, and reminded once a week while
+  another location is still backed up, or every day when none is.
 - A file or folder that is left out because of its name now gets a notification of its own, in the
   log and in `occ backup:run`. It says the item is missing from the backup, gives example paths and
   asks to rename it; before, it was reported as unreadable, with advice about permissions.