Fix console errors with popover-link-component.

This technique is similar to how I'm doing all scroll debouncing in my app. I brought over the mixin I'm using and utilized it here. This resolves #71.
I realize this is different than how you're doing the other bindings, and I'm open to other ways to handle the issue, but this was the way I fixed it locally on my project.

Also, here's [a clone utilizing my new code](http://jsbin.com/jewati/2) of the [original JSBin](http://emberjs.jsbin.com/xabeb/1) that exhibited the problem. You'll note that that the error is now fixed (no errors in the console, and debounced snapping still working).
This might be better off as ```_debounce``` and to use it in the legacy [```debounceSnapToPosition```](https://github.com/Addepar/ember-widgets/pull/75/files#diff-0ef35dc1398db4aad9cae8fc094d2428R176) method. Again, wanted to limit the scope of my changes.