Format settings file

See this answer https://stackoverflow.com/questions/22950542/pretty-printing-xml-with-jackson-library

src/main/java/name/nathanmcrae/numbersstation/MainSettings.java

@@ -110,6 +110,7 @@ public class MainSettings {
         XmlMapper xmlMapper = new XmlMapper();
         xmlMapper.registerModule(new JavaTimeModule());
         xmlMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
+        xmlMapper.enable(SerializationFeature.INDENT_OUTPUT);
         try {
             Path filePath = getSettingsFilePath();
             Path directoryPath = filePath.getParent();