created email validator

[jrushlow]

validated an email address using PHP's filter_var method else throw a RuntimeCommandException

use case: reset-password-bundle

[weaverryan]

@jrushlow Can you just put this into #567 if we need it? That way we can see it in context there :)

[jrushlow]

sounds good to me.. i think we talked about that before too..

will close PR after updating 567