Allow devtools properties in user.home

Support loading a `.spring-boot-devtools.properties` file from the
users home folder. The property file can be used to customize settings
that make sense on a per-user basis, but might not want to be checked
into the project.

Fixes gh-3151

spring-boot-samples/spring-boot-sample-devtools/src/main/java/demo/SampleDevToolsApplication.java

@@ -26,4 +26,5 @@ public class SampleDevToolsApplication extends WebMvcAutoConfigurationAdapter {
 	public static void main(String[] args) {
 		SpringApplication.run(SampleDevToolsApplication.class, args);
 	}
+
 }