Improve the Measurement Aggregation Toolkit

[sarathms]

We have started working on a generic web-based tool that can help with creating useful visualizations with aggregated measurement data from the API. It is currently deployed in the experimental garage of OONI Explorer. (https://explorer.ooni.org/experimental/aggregation). The interactive one is currently here (and will be moved to the earlier link).

With @hellais, we discussed a bunch of improvements we can do for the next iteration:

• Rename to experimental/aggregation
• Add drop-down for probe_cc, category_code
• Date selector
• Replace domain with input
• Add query params to URL bar
• [ ] Add support for axis_y plotting
• [ ] One heatmap each for anomaly_count and confirmed_count
• • [ ] Build upon that a single heatmap with both values in each cell