Allow user to control when date headers are shown

[seunghyeoks]

I wanted to have the time sent displayed next to the message bubble, so I made the bubbleBuilder display the time via the bubble package.

So I want to turn off the DateHeader that Chat creates every 15 minutes. I only want it to be displayed if the date has changed.

For now, I set the dateHeaderThreshold to one day (24 x 60 x 60 x 100), is this okay?

If you have a better way, please let me know!