LAPPS-30 AppArtifact and ArtifactType added
Merge remote-tracking branch 'origin/app_domain_model' into
app_domain_model

Conflicts:
	LAPPS-backend/src/main/java/de/rwth/dbis/layers/lapps/entity/AppEntity.java
	LAPPS-backend/src/main/resources/META-INF/persistence.xml
	LAPPS-backend/src/test/java/de/rwth/dbis/layers/lapps/domain/AppFacadeTest.java
	LAPPS-backend/src/test/resources/META-INF/persistence.xml