New more configurable version of JMX exporter, using simpleclient.

It supports:
- Scraping the local jvm
- Scraping a remote jvm
- The existing output format by default (mostly, escaping is a bit safer, and it doesn't assume 'type' is the first beanProperty)
- Customising the name, help and labels as needed
- Exporting only what you want (only whitelist right now, blacklist would be easy to add)
- The java simpleclient

A config of 
  { "hostpost": "localhost:1234",
    "rules": [
      {"^java"}
    ]}
would export everything under java, with the default (i.e. existing) format.



I haven't written tests or the servlet bit yet, but wanted to get initial feedback on the approach.
It also puts out a metric per sample too rather than combining metrics with the same name, which isn't correct.
> What would you call something that exports metrics to JMX?

I'll put that on my TODO list once it arises.

Sure, we might come to the conclusion that we should better rename everything, but I don't want to rename everything right now.