Added a midnight divider line on the graph to visually separate days.

[sslater11]

I've added a little divider so we can see when we scroll to another day's forecast.

I'd like the day to be separated more. Maybe we could change the background colour for tomorrow's forecast?

Warning: To keep the code simple, I get the hour from the label strings. If you implement AM/PM into the labels, it would break this feature.

The midnight line will go in front of the rainfall and behind everything else, like the temperature line.