Updatable notifications

One useful feature would be updatable notifications. When processing alerts from CCTV you might have an initial "something's happening" alert, which would then be followed some time later by an image which might get refined to a more accurate image or video a bit later.

Having Pushover accept all of these notifications but instead of creating individual alerts, it could update the original notification to include the additional data as it arrives would be a useful feature. This could be done by supplying an optional, unique notification ID in the API call which would identify that subsequent follow-up messages are updates for the original notification, so the basic API function is unchanged and it would be relatively easy to retrofit.