Feature/#422 dedicated transport_l layer for air traffic

Created by: das-g

closes #422 (closed)

Reviewed by

• @hixi
• @sfkeller (for the SQL)
• @beneditatan

You might want to review 7ff86a4f and 36778880 separately, as GitHub's overall diff view doesn't recognize that *_air_traffic.sql is the same (moved and modified) file.