New survey checkErrorsMode, onValueChanging

[andrewtelnov]

We have a popular onValueChanged check error mode, when a user can see an error on changing the value and not on click "Next"/"Complete" buttons, the default behavior.
onValueChanging is similar to onValueChanged, except one big difference. If the value is incorrect, there is an error, then value will not set into survey data. It means that survey data will not contains data with validation errors.
In this mode, you should be aware that question.value and survey.getValue("questionName") can be different, if the question value is not valid. question.value contains value entered by end-user.