Add unit

Add unit in both Y axis and tooltip display

Apache ECharts offer the availability to add a unit formatter.

There are two functions to provide. One for Y axis and one for the tooltip:

                yAxis: {
                  axisLabel: {
                    formatter: "{value} °C" 
                  }
                },
                tooltip: {
                  formatter: function (params) {
                    return (
                      Math.round(params[0].value * 100) / 100 + " °C"
                    );
                  }
                },