Support loading view tag name + cleanup

Apologies if the __loadingViewAttributes stuff was necessary, however
this seems like a cleaner way to initialize the LoadingView.

As a side effect, the LoadingView now supports tag name as explicitly
passing a `<div>` as the LoadingView's element would override this.
Merge pull request #1 from ajbeaven/support-tag-name

Support loading view tag name + cleanup