Fixed PHP error that could occur if requiring No Duplicates and Email Confirmation on fields.
Updated Validation_Result::add_reason() to be a public method.
Added filter to enable/disable Enable Email Validator setting. (#5)
Added gpev_disable_email_validator_by_default PHP filter hook to disable validation by default.
Added support to block/allow specific top-level domains (e.g. .ru).
Internationalized "Only Visible to Form Editors" so it can be translated.
