Collect the number of services polled and the number of automations ran via JMX

Here we add a counter to the scheduler that keeps track of the number of tasks (ReadyRunnables) executed.

Using this counter makes it easy to expose service-specific statistics via JMX and have these collected using the existing OpenNMS-JVM collector.

In this case, we use it specifically for exposing the number of polls executed by pollerd and the number of automations executed by vacuumd.