feat: add NKEYs and JWT auth

[mja00]

This adds support for authenticating using NKEYs and JWT following this part of the nats.js readme.

This was tested using the following as the app.js

'use strict';
const _ = require('lodash');
const spawnpoint = require('spawnpoint');
const app = new spawnpoint();

app.setup();


app.on('app.ready', function() {
	console.log('App is ready');
	// Run the following every 5 seconds
	setInterval(function() {
		// Publish a message to the NATS server
		app.nats.publish("test.1", "I'm test 2!", function() {
			console.log("Message sent!");
		});
	}, 5000);

	// Subscribe to test.1
	app.nats.subscribe("test.2", function(msg) {
		console.log("Received a message on test.2: " + msg);
	});
});

And the following as the nats.json

{
	"connection": {
		"tls": true,
		"maxReconnectAttempts": -1,
		"timeout": 10000,
		"auth": {
			"creds_file": "default.creds"
		}
	},
	"request_defaults": {
		"timeout": 5000,
		"maxMessages": -1,
		"maxWait": -1
	},
	"subscribe_prefix": ""
}

Spawnpoint was able to successfully connect and communicate over NATS.

[mja00]

Not sure if this is redundant as I delete the entire object on line 65 but included just in-case.

[Cherry]

This looks great, thanks Matt!