submit() never fires if any element is missing validation attributes

[danielbodnar]

validateElement() returns an undefined (on line 46 of validationManager.js) if element doesn't have any validation attributes on it (e.g.: required, min-length, etc).

Fix is to apply a default value to isValid on line 18.

[jonsamwell]

Thanks for finding and solving the issue! I've just added a few unit tests around this to prove the functionality. Awesome work!