Collect metrics statistics from servers

War now collects statistics from servers running the plugin. The statistics are minimal. The goal is so the developers of the plugin can tell what areas they need to do more work in.
In addition to the default statistics collected by PluginMetrics, War sends the number of warzones and if certain plugins that War interfaces with are enabled.
To prevent your server from sending statistical data, set "opt-out" to "true" in plugins/PluginMetrics/config.yml.
Closes #716.
Merge branch 'metrics'