GROOVY-6268: Added 'Working with JMX' section

Some qestions and comments:

- links were replaced:
 - http://java.sun.com/javase/technologies/core/mntr-mgmt/javamanagement -> http://www.oracle.com/technetwork/java/javase/tech/javamanagement-140525.html
 - http://edocs.bea.com/wls/docs100/wlsmbeanref/index.html -> http://docs.oracle.com/cd/E13222_01/wls/docs90/wlsmbeanref/core/index.html
 - http://java.sun.com/j2se/1.5.0/docs/guide/management/jconsole.html -> http://docs.oracle.com/javase/1.5.0/docs/guide/management/jconsole.html
 - http://static.springframework.org/spring/docs/2.1.x/reference/jmx.html -> http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/jmx.html
 - http://blogs.sun.com/sundararajan/entry/groovier_jconsole -> https://blogs.oracle.com/sundararajan/entry/groovier_jconsole

- Oracle stopped support OC4J and link to OC4J (http://www.oracle.com/technology/products/oc4j) is broken. And also, examples with OC4J cannot be compiled, because need third party dependencies. Now, these examples inserted in the page as is.