'requiredError' Common Field Property

User Story

As a Form Designer, I can define the error to be displayed if a user fails to enter a required field, so the fact that the field is required is clear to the user.

Acceptance Criteria

1. In a Form Model, the 'requiredError' property can be optionally defined for a data field, that defines the error message that should be displayed is the user fails to enter a value.
2. When the form is rendered, if the data field is required #130 and the user fails to enter a value:
   a. If the 'requiredError' property is defined, the custom required error message is displayed.
   b. If the 'requiredError' property is not defined, a generic required error message is displayed.

Dev Notes

• requiredError defined as a thing allowing the error messages in multiple languages to be defined:
  ui:requiredError [ rdfs:label "Social Security Number (SSN) is required"@en ] ;