Experiment with generic debouncing code

[aaronlehmann]

The dispatcher implements debouncing when sending and receiving task updates.

The scheduler implements debouncing on commit events.

We should look into having a common implementation of "coalesce the following events that happen with a gap up to X ms between then, with a maximum latency of no more than Y ms". This could be tested intensively and avoid code duplication.

[stevvooe]

https://godoc.org/golang.org/x/time/rate is a solid package for generalized rate limiting.

This is also a model I'd like to see in go-events: coalesce events into N sized blocks with limited delay (say 100ms or 10ms).