Add support for field format validation

[iamEAP]

The 1.x addressfield.json configuration schema provides for a "format" property on field configuration objects, representing a regex pattern for validation:

{
  "label": "State",
  "options": [],
  "format": "^[a-zA-Z]{2}$"
}

We should provide (optional) integration with a form validation framework based on any provided values. Probably https://github.com/jzaefferer/jquery-validation.