Caches should have metrics by default

The platform caches have no metrics:

<component
  name="com.mycompany.mycomponent.caches">

  <extension target="org.nuxeo.ecm.core.cache.CacheService" point="caches">

    <cache name="mycomponent-cache" class="org.nuxeo.ecm.core.cache.InMemoryCacheImpl">
      <!-- one day -->
      <ttl>1440</ttl><!-- minutes -->
      <option name="maxSize">500</option>
    </cache>

  </extension>

</component>

It makes sense that metrics may be exposed automatically for every cache that is configured on the platform (request count, hit rate, etc.). Our metrics are implemented using "Coda Hale Yammer Metrics" (See: https://doc.nuxeo.com/display/ADMINDOC710/Metrics+and+Monitoring).

Work will be done in Studio/Connect to implement that automatic metrics creation. Based on that, it might be adapted and implemented in the platform. Studio/Connect will then be able to rely on it, and remove the code as it will be superfluous.