Add grouping logic for voltage disturbances

[prestoncraw]

Summary

• Groups overlapping voltage disturbances by event type, including singleton groups.
• Adds per-type group badges, colored borders, and a separate Worst status badge.
• Uses backend-compatible group numbering and stable start-time ordering.

The grouping follows openXDA's Range<T>.MergeAllOverlapping, as used by VoltageDisturbanceAnalyzer.GetDisturbanceList.

Screenshot