Adding monitoring of ActiveMQ for the EhCache topic.
Added the following counters:
* AverageEnqueueTime
* BlockedProducerWarningInterval
* ConsumerCount
* DequeueCount
* DispatchCount
* EnqueueCount
* ExpiredCount
* InFlightCount
* MaxEnqueueTime
* QueueSize
* ExpiredCount
* ProducerCount

Note - there is a problem with the path when adding these metrics to a custom dashboard, 'null' needs to be added in the path,
i.e. : 'JMX/org.apache.activemq/*null*/Topic/ehcache/messageQueueService/ExpiredCount'