constructor () {
		this.plugins = [];
	}
Wrapper class around RLS-scoped ReactServerAgent plugins to avoid
a circular dependency between ReactServerAgent and ReactServerAgent/Request.

Note: It's possible that this module shouldn't exist at all. ReactServerAgent
plugins maybe shouldn't be request-scoped; they could be set statically,
and get their data from RLS if they wanted, instead. i.e., store something
in RLS, then have the plugin retrieve it, and that way the code being
executed is the same for _all_ requests)