Fix destroy:composer event not being fired

[jrhames]

This pull-request fixes two issues:

• The destroy:composer event is not being fired when the node is removed, as addEventListener only accepts a string as type;
• The destroy:composer event is not fired if any of it's parents is removed from the document.

Please, note that:
The DOMNodeRemoved has been kept to cover the case where the element is removed from a currently detached parent.

[pulges]

Thanks for finding and taking time to address the issues.
Allthough it is a valid fix of current code I have a doubt merging it to master though. The problem is that mutation events (DOMNodeRemoved and DOMNodeRemovedFromDocument) are labelled as deprecated and browsers support is in process of being removed.
https://developer.mozilla.org/en-US/docs/Web/Guide/Events/Mutation_events

It would be awsome if you could make it using the new mutation observers instead:
https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver

The MutationObserver needs a setTimeout polyfill though if not supported by browser (IE 9-11), but the setTimeout hack is currently used as fallback anyway so it would not be a regression.
https://github.com/Voog/wysihtml/blob/master/src/views/composer.observe.js#L541