Metricset xml configuration

Created a simple metricset configuration. 
NOTE: no unit tests created, but it works. If you pull this in I can write unit tests. 
NOTE2: this also has the changes for allowing property placeholders

    <metrics:metric-registry id="metricsRegistry" name="springMetrics" />

    <metrics:reporter type="jmx" metric-registry="metricsRegistry" duration-unit="MILLISECONDS" rate-unit="SECONDS" mbean-server-ref="mbeanServer"/>
    <metrics:reporter type="graphite" metric-registry="metricsRegistry" period="${graphite.periodInSeconds}s" host="${graphite.host}" port="${graphite.port}" duration-unit="MILLISECONDS" rate-unit="SECONDS" prefix="${graphite.prefix}"/>

    <!-- annotation-driven must be included in all context files -->
    <metrics:annotation-driven metric-registry="metricsRegistry" />

    <metrics:metric-set metric-registry="metricsRegistry" ref="garbageCollectorMetricSet" name="jvm.gc" />
    <bean id="garbageCollectorMetricSet" class="com.codahale.metrics.jvm.GarbageCollectorMetricSet"/>

    <metrics:metric-set metric-registry="metricsRegistry" ref="memoryUsageGaugeSet" name="jvm.memory" />
    <bean id="memoryUsageGaugeSet" class="com.codahale.metrics.jvm.MemoryUsageGaugeSet"/>

    <metrics:metric-set metric-registry="metricsRegistry" ref="threadStatesGaugeSet" name="jvm.thread-states" />
    <bean id="threadStatesGaugeSet" class="com.codahale.metrics.jvm.ThreadStatesGaugeSet"/>

    <metrics:metric-set metric-registry="metricsRegistry" ref="fileDescriptorRatioGauge" name="jvm.fd.usage" />
    <bean id="fileDescriptorRatioGauge" class="com.codahale.metrics.jvm.FileDescriptorRatioGauge"/>