Zooming on the graph causes predicted values to change

[baobabKoodaa]

Hey, I really love this calculator and I think this is an amazing piece of work! I noticed this minor issue and I would be happy to provide a PR for it if you'd be interested?

I noticed that the generation of values is tied to the presentation of values (to be specific, it's tied to the timestep/zoom of the graph). For example, using the default parameters and default zoom, day 100 infected count is 66,006. But if you zoom in on the graph so that day 100 is the last day shown, the infected count changes and is now 66,977. This appears to happen because, although the label says "day 100", it might actually be "day 100.38" (or whatever, depending on the timestep).

I think generation of values should be entirely separated from the presentation of values: generate values for all the days and then show values for the desired days. With this change the predictions don't change depending on the zoom. This change would also require tweaking the way zooming works on the graph.