fixed deleting of a database

fda-database-service/services/src/main/java/at/tuwien/service/DatabaseService.java

@@ -61,6 +61,7 @@ public class DatabaseService {
         return opt.get();
     }
 
+    @Transactional
     public void delete(Long databaseId) throws DatabaseNotFoundException, ImageNotSupportedException,
             DatabaseConnectionException, DatabaseMalformedException {
         log.debug("get database id {}", databaseId);