Forms, image widget

* Added validating image widget
Forms, validation

* Form checks error count
Forms, render classes

* Form renderer adds 'valid/invalid' class to inputs
Forms, validations

* Added select, radio and multicheckbox value range validation
Forms, rendering validation

* Renderer adds valid/invalid classes only after submitting
Forms, datetime validation

* Fixed datetime widget validation
Forms, widget validations

* Fixed reporter str from widget validation