All the FredPlugin* APIs must be implemented by the main class - the class that implements
FredPlugin, because that's where we look for them when loading a plugin. That allows us to
automatically register the plugin for whichever service it is using.
Run the plugin. Called after node startup. Should be able to access
queue etc at this point. Plugins which do not implement
FredPluginThreadless will be terminated after they return from this
function. Threadless plugins will not terminate until they are
explicitly unloaded.