Add logback-parent to dependency management and use a consistent slf4j version everywhere

pom.xml

@@ -147,6 +147,13 @@
 				<artifactId>gson</artifactId>
 				<version>2.8.5</version>
 			</dependency>
+			<dependency>
+				<groupId>ch.qos.logback</groupId>
+				<artifactId>logback-parent</artifactId>
+				<version>1.2.3</version>
+				<type>pom</type>
+				<scope>import</scope>
+			</dependency>
 		</dependencies>
 	</dependencyManagement>