Setting nuiClass on a view should force NUI to be used, regardless of subclassing status

The use case that led to this change is the following:

I have a custom UIView subclass, within that are a number of UILabels where I'd like to use NUI. Previously, since they were embedded in a UIView subclass, NUI would skip over them and not apply a style. This change will now let them use NUI, if a nuiClass is explicitly set.

This change has also been applied to similar checks in UIView, UIControl, UISlider, UISwitch (+NUI.m)