Internal event queue for async added destination

[alexanderkirtzel]

Is your feature request related to a problem? Please describe.
While loading the walker.js and destinations all asynchronously in a browser, one could not guarantee the loading order.
When the walker.js runs first and triggers the first events like a page view and later a slowly loaded destination gets added, it will not receive the event. That makes me sad.

Describe the solution you'd like
A clear and concise description of what you want to happen.
During a run, events should be stored in memory to be shared with async-loaded destinations. If a destination is added later, I want an option to disable the push of previous events.

[alexanderkirtzel]

Use destination.config.queue = false to disable processing