Cleaning up fieldProps

[alvinsj]

There are many unclear key in fieldProps.

e.g.

1. how is defaultValue, value, error is computed?
2. what is error, field?

const fieldProps = assign({}, def, {
      ref: c => {
        this.fields[refName] = c;
      },
      // key: refName,
      className: 'field',
      field: def,
      name: name,
      value: value,
      defaultValue: defaultValue,
      label: label,
      error: error,
      disabled: disabled
    });