Update form validation states

Update form validation states

* Once again no longer applies to single inputs (this is a bit simpler,
but I'm open to new ideas) but the entire set of inputs, labels, and
help text within a particular element. However, the styles are not too
dependent on markup or layout, so they're super flexible.
* Simplified the markup in the validation docs examples to match latest
changes.
* Renamed `.form-state-validation` mixin to `.form-control-validation`
to match naming of prev commit.