[Enhancement] Live Validation for Email Input

[OwenMelbz]

summary
Displays a tick or cross next to email address fields if email_validation is set to true

preview

usage

$this->crud->addField([
    'name' => 'email',
    'label' => 'Email Address',
    'type' => 'email',
    'email_validation' => true
]);

[tabacitu]

@OwenMelbz I don't think we should include this in the core (again, it does things differently than the other fields), but I'd love to feature this on the Backpack for Laravel blog, in the Code Snippets section, as a separate field people might be interested in, say... valid_email. That way people can reuse your code, still in an "official" manner, and you'd get a link towards whatever you want to promote :-)

What do you think, are you interested in writing an introduction paragraph and collaborating on a GoogleDoc/smth, so we can post on the blog?

Thanks, cheers!