Unmounting ReactPIXIComponent does not destroy internal Display Object instance

[michalochman]

The unmountComponent method should at least call destroy method with { children: true } as an argument and probably unset internal _displayObject property – there is no need to keep a reference to these after component is unmounted:

var CommonDisplayObjectContainerImplementation = {
    ....
    unmountComponent: function unmountComponent() {
        this.unmountChildren();
+        this._displayObject.destroy({ children: true })
+        this._displayObject = null
    },
    ...
};

Not calling destroy on this._displayObject causes a memory leak.

I suppose we could also reset all properties that are assigned in the mountComponent method.

[michalochman]

@Izzimach do you think you will be able to release the above this week on npm? Same question for #89.