Merge branch 'rs-disables-submit-behavior' into 'master'

Add "Requires Input" JS behavior

This aims to replace all of those `disableButtonIfEmptyField` calls littered throughout views and JS with a simple, clean, markup-based behavior.

While going through all of the old usages, I found a few places where the old behavior wasn't actually working, so... bonus, they work now!

See merge request !900