Swap priorities of v2 and v3 API media types

Priortizing v3 caused problems for v2 clients on POST requests.

src/main/java/de/thm/arsnova/config/AppConfig.java

@@ -125,8 +125,8 @@ public class AppConfig extends WebMvcConfigurerAdapter {
 	@Override
 	public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
 		converters.add(stringMessageConverter());
-		converters.add(defaultJsonMessageConverter());
 		converters.add(apiV2JsonMessageConverter());
+		converters.add(defaultJsonMessageConverter());
 		//converters.add(new MappingJackson2XmlHttpMessageConverter(builder.createXmlMapper(true).build()));
 	}