Add ability to batch notifications on rapid-fire messages

[LeftyBC]

If someone sends X messages within X seconds, they should be batched into a single notification. This avoids notification storms.

[halkeye]

I think I figured out a way to do this easily, I just don't know what the messages should look like when batched.

Just newline separated? batch up to 30 seconds?

[LeftyBC]

Yeah, I think newline separated would be find.

As for the time - 30 seconds is probably a reasonable default, and possibly a configurable?