Feature/plotting time vs concentration using d3 library

Code integration with D3.js library. The plot "Mean concentration of infectious quanta" is now a svg component of the /calculator/report page. The main changes is that we build the plot component by component, using d3 methods for the svg elements:

1. Title
2. Presence of exposed person(s) area
3. Breaks
4. Axis and respective labels

The new report.js file has all the logic behind the plot's construction.

Right now the boundaries variable is passed from the model to the frontend side so that we can paint the presence intervals in the plot.

The plot considers the data that comes from the model - times and concentration. The x axis has a transformation to display the time of day in H:M format.