Final text review

@AlasdairSwan and @wedaly, these are copy changes suggested by @srpearce. I've also modified the field validation utility to use the field's `label` in error messages instead of the field's `name`; the `name` is used primarily for styling, isn't i18n'd, and isn't necessarily consistent with the field `label`.
Done. The new function is `_fn.validate.getLabel`.