OnVerificationCodeChanged listener and ClearOnSubmit flag

[kkartal]

There isn't any listener for verificationCode.

• onSubmit is triggered when verificationCode matches the predefined conditions.
• onCodeChange gives only the latest char.

I added onVerificationCodeChanged and it's triggered when verificationCode is changed. null values are filtered, so, this function returns only non-null values.

[kkartal]

I wanted to clear all fields when user types wrong code.

• There is a "clearText" flag currently but it does not work properly and efficiently. Also, it's for manual update.

I added a flag if the code will be deleted when the onSubmit function is called.

[ainulbedjo]

LGTM