Better default zoom of trend plots

[tommasobonomo]

As the timeframe of COVID-19 in Italy is (unfortunately) becoming quite long, instead of cramming the whole history of the plot as the default view, it might be better to enable a few features. Specifically:

• Default zoom that shows the most recent updates
• Possibility to change the default zoom (only on the x-axis? or also the y-axis?)
• Panning possibility when zoomed in (it's already implemented if keeping zoom on both axis, must change if restricting to x-axis)