Silence Deprecation Warning When Registering as Service

[jherdman]

Ember 1.13+ isn't thrilled that the resize service is being registered
as a service factory, but isn't extending from Ember.Service, or being
indicated as such.

This change resolves this deprecation. I opted not to extend
Ember.Service as that'd break users of this addon that are stuck on
Ember pre 1.10.

[walter]

Given that this solution fails for ember beta and ember canary, I wonder it makes more sense to make it a Service. Users that are stuck at pre-1.10 can freeze which version of the ember-resize addon they are using. They are certainly going to have to do that for a lot of addons already.

[mike-north]

I think this PR is failing because of how the view registry changed in 2.0. I can apply a fix to master and re-trigger this PR

[jasonmit]

Conditionally extend from Ember.Service if it's available. That should remove the warnings while still supporting older versions of Ember.

const Base = Ember.Service || Ember.Object;
export default Base.extend(Ember.Evented, { ... });

[jherdman]

@jasonmit's solution seemed reasonable to me, I've updated the pull request accordingly.