Source credits for received traffic; update source-priority rules

Open Waters AIS keeps source and licensing credits available to Signal K apps receiving traffic.

Upgrade: If your source-priority rules match signalk-aiscast.net exactly, add the relevant per-feed names shown in Signal K's Data Browser. The old name does not match the new feed identifiers.

• Received traffic identifies each upstream feed, with volunteer stations grouped by source prefix. Apps can read source, license, and attribution at each target's sensors.aiscast path and match credits to fields with a source. Plain identity fields such as name and callsign use the target's combined credits. #321
• The NMEA output setting and README explain that chartplotters need credits displayed separately: NMEA 0183 and NMEA 2000 cannot carry the attribution text. #321