refs https://github.com/TryGhost/Team/issues/874
- when hit with focus on last non-empty benefit field, previously the new benefit automatically showed error for empty field. This change refines behavior to only show error when user tries to click "Enter" again when already on last empty benefit
- also cleans up the duplicate add benefit call
refs https://github.com/TryGhost/Team/issues/874
In the product benefits modal in Admin, hitting Enter has been updated to work as -
- when hit with focus in an empty benefit field: does nothing
- when hit with focus in any field outside benefit fields: does nothing
- add new benefit and focus on it when hit while on a non-empty benefit
refs https://github.com/TryGhost/Team/issues/792
- updates product benefit to use `name` instead of `label` attribute for benefit text
- updates model/serializer/validator to correctly handle benefit attributes
- added `+` button for adding new labels as the enter behavior is closing the popup(needs fix)
