Visualize aggregated quality results on the bbox

[MarcoMinghini]

In addition to the qualitative visualization of the intrinsic quality of single OSM nodes and ways, it would be good to start including some quantitative metrics of intrinsic quality, computed by aggregating the results for each of the quality elements investigated.

As an example: for the date of creation of OSM nodes/ways, a starting point can be to add a plot or pie chart showing the aggregated behaviour (by dividing the range of dates of creation into classes), plus aggregated statistics such as the mean and meadian date of creation (+ standard deviation).

This would improve the overall understanding of OSM intrinsic quality that the web application is able to get from the data.