Changed to not useInteractiveGuideline to allow tooltip content change.

useInteractiveGuideline overrides all of the nice functions like tooltips() and tooltipContent() that you can use to modify the content of tooltips. I've remove useInteractiveGuidelines and then changed the tooltip to be something we want to display.

I've also moved the time stringing function to a utility so it can be used by both the graph and the time slider.