Clobbering `this` from `options` might be murky

If I understand [the constructor](https://github.com/ember-cli/core-object/blob/9138b1f55da74386b9547110ee5b6f52afcdfa65/core-object.js#L18-L20) correctly, we're providing the ability to assign arbitrary properties on `this` through an `options` hash as a common base class constructor.

I used to do this in early versions of Broccoli plugin classes because it seemed convenient. I stopped doing it when I started running into cases where some library upgrade would cause property names to start colliding with option names. I simply do `this.options = options` in constructors ever since, and have been much happier with that.

My suggestion would be to make the base class constructor empty, and let people do their own option handling. I realize this might be a breaking change, but perhaps it's worth considering for the next major version?