Correction des images pour ajouter un fond blanc

src/main/java/app/SimulatorApplication.java

src/main/java/controller/Controller.java

.../model/doctorviruspatient/DoctorVirusPatientScenario.java

src/main/java/view/FirefighterGrid.java

src/main/resources/view/icons/fire/avion.png

src/main/resources/view/icons/fire/camion.png

src/main/resources/view/icons/fire/flamme.png

src/main/resources/view/icons/fire/montagne.png

src/main/resources/view/icons/fire/nuage.png

src/main/resources/view/icons/fire/rochers.png

src/main/resources/view/icons/fire/sapeur-pompier.png