Added events to smoothie charts

[francobottero]

It's important to say that events have to go on a separate TimeSeries than the rest of the data or else, they will interfere with the chart. Events will look something like this :

[cinderblock]

@francobottero Have you considered updating this to use a separate TimeSeries type? I for one would like to see this feature added.

[drewnoakes]

@cinderblock feel free to create a new PR if you have the bandwidth.