Merge branch 'Ying' into 'master'

src/main/docker/sonar/docker-compose.yml

src/main/java/de/rwth/swc/sqa/DataService.java

src/main/java/de/rwth/swc/sqa/api/CustomerController.java

src/main/java/de/rwth/swc/sqa/api/TicketController.java

src/test/java/de/rwth/swc/sqa/sqa/CustomerTest.java

src/test/java/de/rwth/swc/sqa/sqa/DemoIntegrationTest.java

src/test/java/de/rwth/swc/sqa/sqa/TicketTest.java