Dom cleanup on destroy

[thecodedrift]

Currently, the destroy() method doesn't clean up any handlers attached to the document object. This both resolves that issue and keeps all listening centralized using the same addEventListener logic.

• adds a property this.allListeners = [] to contain all registered DOM listeners
• adds a method this.addListener(obj, on, fn) to centralize DOM listener registration
• adds a method this.removeAllListeners() which removes every listener in the allListeners collection, invoked in destroy() before viewport.destroy()