yii.activeForm.js refactoring/enhancements

[SilverFire]

Originally suggested by @DmLapin here: https://github.com/yiisoft/yii2/issues/10549#issuecomment-227441454

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There are few potential places for changes, but it can break compatibility (may be it could be included in 2.1 milestone):

• validate() should validate regardless of field.state or form.submitting and trigger appropriate events like before/afterValidate
• updateInputs() should work only with error messages, as it's doc says and should not watch for internal form state and should not submit form by self.
• my logic tells me that validate() method should call validateAttribute() during its operation but not vice versa.
• replace status = 1 / 2 / 3 (if activeForm really needs it) with comprehensible variables like STATUS_VALIDATED / STATUS_WAIT_FOR_VALIDATION / ...

But at current moment at least validate() and updateInputs() methods should be fixed to perform validation properly and trigger afterValidate event in case of manual call.

[alex-code]

If things are being enhanced it would be nice if validateAttribute could return a promise so you can have a complete callback.

e.g

$('#my-form').yiiActiveForm('validateAttribute', 'attribute').done(validated => { });