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.
matching one format for rules and another for exported format might be hard for users to reason about unless it can be well documented.