[#99] Basic Health Metrics

Changes following review
    - Reusing CounterService to automatically profit from Dropwizard if present
    - NoOp is the default impl for SpanReporterService
    - SpanReporterService has configurable metric names (it's enough to change the
    name to 'meter.a.b.c' to profit from Dropwizard's meters)

    Fixes gh-99

spring-cloud-sleuth-samples/spring-cloud-sleuth-sample/pom.xml

@@ -52,10 +52,6 @@
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-aop</artifactId>
 		</dependency>
-		<dependency>
-			<groupId>org.springframework.boot</groupId>
-			<artifactId>spring-boot-starter-actuator</artifactId>
-		</dependency>
 		<dependency>
 			<groupId>org.projectlombok</groupId>
 			<artifactId>lombok</artifactId>