Modelize Mixin needs refactored

[notmessenger]

https://github.com/softlayer/sl-ember-modelize/blob/master/addon/mixins/modelize.js#L37

For example, "normalizedKey" should not be declared where it is.

[notmessenger]

https://github.com/softlayer/sl-ember-modelize/blob/master/addon/mixins/modelize.js#L42 could be replaced with use of http://emberjs.com/api/#method_keys too