Tweaking how future date validation works

The attribute for validation was hard-coded. I believe this was an
artifact of copying the validator from another repository.

While doing this, I removed the custom class, instead creating a
dynamic class that can be disposed of at the cleanup's leasure.
Merge pull request #528 from ndlib/fixing-multi-value-collection-input

Array#wrap of multi-value input collection
Merge pull request #533 from ndlib/fix-validation-text-for-future-date

Tweaking how future date validation works
Merge branch 'develop' into update-article-metadata

* develop:
  Tweaking how future date validation works