Fixes#350 and fixes#404
This change abandons validation via EditableFormField::validateField, as it bypassed too many core validation mechanisms (RequiredFields, etc).
In order to enforce consistency of editable field validation, display rules have been hard-disabled when a field is marked as required.
Since this removes functionality, I have incremented the major version number
Construct adds extensions, so calling functions which have extend calls in them before the parent:constructor means the extend calls will never find any extensions.
- Page no longer reloads on new field
- Preview mode no longer errors on new field
- Sort order of field dropdown is ordered
- Default field type to Text field instead of abstract base class
- Ensure fields named 'Field' is invalidated.
