Merge branch 'develop' into 'tests-airline'

# Conflicts:
#   airlines-module/src/main/java/cz/muni/fi/pa165/airportmanager/airlinesmodule/data/model/Airline.java
#   airlines-module/src/main/resources/application.properties
#   flight-module/src/test/java/cz/muni/fi/pa165/airportmanager/flightmodule/service/FlightServiceTest.java