Fix merge conflicts

.gitignore

README.md

build.gradle

...l/tudelft/ewi/queue/controller/ErrorControllerAdvice.java

.../tudelft/ewi/queue/controller/NotificationController.java

src/main/java/nl/tudelft/ewi/queue/model/Group.java

src/main/java/nl/tudelft/ewi/queue/model/Subscription.java

src/main/java/nl/tudelft/ewi/queue/model/User.java

src/main/resources/application.properties.template

src/main/resources/changeLog-h2.yaml

src/main/resources/changelog-master.yaml

src/main/resources/changelog.yaml

src/main/resources/migrations.yaml

src/test/resources/application.properties