[bugfix] Handle super calls in CP - WIP

[ssutar]

This PR fix the issue to handle _super calls in CP

For example in below code

const Foo = EmberObject.extend({
      first: "rob",
      last: "jackson",

      fullName: computed("first", "last", function() {
        return `${this.first} ${this.last}`;
      })
    });

    const Bar = Foo.extend({
      githubAlias: "rwjblue",
      fullName: computed("githubAlias", function() {
        const fullName = this._super();
        return `${fullName} [ ${this.githubAlias} ]`;
      })
    });

    let obj = Bar.create();
    const fullName = get(obj, "fullName");

The fullName is undefined [ rwjblue ] whereas it should be rob jackson [ rwjblue ]

[ssutar]

This will fix the issue #15

[pzuraq]

Tests are passing but Travis never reported back, going to merge