Consistent X-axis regardless of data availability

[dsjoerg]

The default behavior of our site is to quietly adjust the x-axis to cover the data range available.

That makes it easy for someone to miss, and misunderstand the chart, and assume that they're seeing data up to the current date when in fact they may be looking only up to March 15th.

Random example: https://visitdata.org/bydatesel/Idaho/Bonner%20County/ALL

So, instead, always make the x-axis go up to the latest date that we have data for.

For regions that have no data, consider adding a shaded region indicating "Insufficient Data Available", which is doable in Highcharts as well.