Migrate to new RCTab format

[artoonie]

The new RCTab format supports per-round thresholds and breakdowns of inactive votes. Use it as the new default format, and migrate all formats to the new format. This includes the previous RCTab format, meaning we'll need a converter from today's RCTab JSON to the new format.

Here is an example of the new format: https://github.com/BrightSpots/rcv/blob/develop/src/test/resources/network/brightspots/rcv/test_data/generic_csv_test/generic_csv_test_expected_summary.json