Toolkit should show filter execution info (what's been filtered out!)

[aesedepece]

To provide a more complete execution trace, the toolkit wrapper should show which data sources where excluded from aggregation when a filter is in use. That is, list which data sources where taken into account and which ones were dropped. This would help detecting and removing faulty data sources that may constantly bounce between being obvious outliers and being just slightly off.

This probably requires changes in witnet/witnet-rust, as the toolkit in this repo is just a JS wrapper.