[data, www] add 3axis graph view

[keomabrun]

For preprocessed datasets with 3 metrics, display multiple graphs.

Example for PDR over each frequency along time: The website should display one graph per frequency (I did not managed to have multiple frequencies on the same graph).

The preprocessed dataset should be under a folder with the following form: metric1_metric2_metric3 Ex: pdr_time_freq

With the following directory tree:

pdr_time_freq/
    11/
        time1.json
        time2.json
        ...
    12/
    13/
    ...