traffic v2.6

Main changes since v2.5 include:

• Detection of events on ground (push back, parking positions, take off runway, etc.)
• Reconstruction of the most plausible flight plan (succession of waypoints)

Minor improvements:

• Support for CSV files downloaded from Flightradar24
• Download and parse METAR information
• Refactoring for altair visualisations
• Switch from cartotools to cartes package
• Many warning fixes
• Documentation improvements