[POC- DO NOT MERGE] Add heatmap for fingerprinting recordings

[microbit-robert]

The output data of the ML filters for each recording are used to plot heatmaps which are effectively fingerprints of the data we pass into the ML model for training and inference. The fingerprints used filter outputs normalized to 0..1, the ML model still uses the non-normalized values and is not impacted by these changes.

These fingerprints are displayed for each recording in the "Add data" page. In the temporary "Process data" page, the fingerprint of the mean of the filters applied to all recordings for each action is displayed, and if a micro:bit is connected, the live data is also displayed as a fingerprint below. The is some alignment issue based on the separation of these plots due to the y-axis labels. This could be dealt with by merging the plots (which would also save space).

We may take this a step further and add functionality to toggle filters. This should be straightforward from a tech perspective, but more complicated from an education and UI/UX perspective.

[github-actions]

Preview build will be at
https://review-ml.microbit.org/fingerprinting

Alternative branches where fingerprints are only shown on the "process data" page:

Fingerprints are shown alongside the existing xyz plots in a 1:1 split (the first fingerprint for each action is the average of all recordings):
https://review-ml.microbit.org/fingerprinting-alt

Only fingerprints are shown (as above, the first fingerprint for each action is the average of all recordings, but this is not clear at all):
https://review-ml.microbit.org/fingerprinting-alt-alt

[microbit-robert]

Closing in favour of #273, but will keep the branch around for demos if required.