Improve Ignore Repeats to work with non-consecutive notifications

[pilot51]

Currently, Ignore Repeats only detects consecutive repeated notifications. This is a problem when, for example, an app is constantly reposting a notification to update a progress bar and a different notification is posted, causing Voice Notify to speak the reposted notification again after the new notification.

This will require a memory of previous spoken notifications up to the value set in Ignore Repeats. If it is set to infinite or a very high value, it could lead to issues with excessive memory usage over time. A good compromise may be to limit Ignore Repeats to something like 24 hours and/or limit the list in memory to 1000 spoken notifications, which should be as good as infinite for practically everyone and even if not, it's better at being infinite than the way it works now.
Be sure to indicate these limits in the dialog.