Channel refactor

[TwinFan]

• Reworked much of the networking code for more robust and independent handling of several channels in parallel.
• Reduced dependency on OpenSky for master data (aircraft type and route information):
  • Reduced aircraft master data lookup, as RealTraffic and ADSBEx nowadays provide good plane type information already.
  • Added new OpenSky Master Data channel for lookup of plane type information, which bases on monthly download of a "database" file rather than individual network requests per plane. Should work even if OpenSky API is down.
• Fixed too many channel switches, especially when ADSBHub was involved in addition to other channels.