Wrap customizer.js in an anonymous function

WordPress uses jQuery no conflict mode, which is why `$` is not available. Rather than reassigning it, we can wrap this JS in an anonymous function and pass `jQuery` to it so that the familiar `$` can still be used.
Remove dependency on customizer-preview

For some reason, when customizer-preview is specified as a dependency, the file is loaded twice and a Javascript error is thrown. Removing the dependency appears to resolve the issue and the functionality of the customizer remains ok.

This resolves the issue where you could not close out of the customizer once it was opened.
Merge pull request #15 from washingtonstateuniversity/js-tweaks

[PR] Modify JS handling so that customizer window will close