Reenable jmx console for easy access

* jminix - unprotected, do not use in production
* Do not use metrics filter on jmx path
Add jetty plugin for convenience
Add servlet for ArithmeticDemoOperation

* Also make operation less boring (non-constant sleep)
* Make similar demo data for jmx less boring
* add servlet to webapp metrics filter
Add Gauge example in the form of a RequestFilter

* Gauge for longest running request
* As a whole it is slightly ugly, due to Yammer not being
  quite as adaptable as I hoped I had to copy some code
* Running a registry of requests as a filter is ugly, it
  would be much better to get to this information by
  calling the Application Container directly (can already
  be done via jmx).
* This is just an example of something a little more
  complex.  Gauge means current - current information
  means having an overview over the system, which isn't
  always easy to come by.
Revise documentation