At/n messaging client

[tavvy]

See https://github.com/Financial-Times/n-messaging-client readme for more info

Why install globally in n-ui?
If the end goal is to have consistent messaging across FT.com then it makes sense that it is an "easy to enable" n-ui feature.

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This demonstrates how the new n-messaging-client could be integrated with n-ui globally.

It would be off by default. To enable an application must invoke n-express with the withMessaging option (which will load the inject the templates and load the presenter). And enable the messaging feature in nUiConfig to load in the client side js.

const app = module.exports = express({
	withMessaging: true,
});

app.locals.nUiConfig = {
	preset: 'complete',
	features: {
		messaging: true
	}
};