Event Rate Limiting

[benfrancis]

Currently in the HTTP Webhook Profile every event must be sent in a separate HTTP request. For very frequent events or property readings (e.g. a temperature value that changes every second or less) this could quickly overwhelm a Consumer.

One mitigation to this problem could be for a Consumer and Web Thing to negotiate the rate of event notifications, or for the Consumer to specify a rate limit when requesting a subscription. E.g. a Consumer might say that it wants to be notified of the temperature reading from a temperature sensor once an hour.

[mlagally]

This seems to be strongly related to #379