fix(local-notifications): Make getPending not return already fired notifications

[theproducer]

This PR adds changes to the local-notification plugin to filter out already fired notifications from the getPending notifications call.

Since Capacitor supports Android API 21+, we can't rely on NotificationManager.getActiveNotifications() to easily get a list of notifications in the status bar. Instead, this PR sets a visible flag on each LocalNotification that gets set when a notification is fired, then cleared when a notification is interacted with.

fixes: #221

[jcesarmobile]

I've tested and it works, but it adds a ton of complexity and I think using storage.deleteNotification when the notification fires is enough to not show it on pending and I don't see any side effects on doing that.
The only thing is have in mind that should only be deleted if not repeatable, so probably should be done inside of the rescheduleNotificationIfNeeded method or make it return a boolean to know if it was rescheduled or not and delete it only if not rescheduled

[theproducer]

Thanks - just deleting the notification worked just as well without any issues!

[jcesarmobile]

looks good

let's wait for next beta before merging so tests pass again (hopefully)