Refactored form validation

FEATURES:

• attributeCaptions section to define custom attributes captions or redefine for entity ones;
• UFormRow: new attributeName prop:
  • automatically get label using metadata and the new attributeCaptions section (see above)
  • automatically show asterisk for required fields using metadata
  • automatically show error text, if value is invalid, including text of custom rules (validateWithErrorText helper, see below)
  • display attribute description if exists instead of name when we hover on the label;
• automate error text for UFormRow, including text for custom validation rules.
  • add new helper validateWithErrorText for defining of attribute validation functions with an error text;
• component-level validations for popup dialogs:
  • add validationMixin for the passing of validation defined locally in some Vue component to nested controls (UFormRow for example)

REFACTOR:

• new provided validator object in Vue instances, with useful helper methods for validation;
• deleted getValidationState provided value since now it is a method of validator;