**ADD TO GRAVITY FORM**
Here is the HTML added  at the top of the form:
<input id="selectall" type="checkbox"> Select all Emails


Here is the sctipt used in the Jquery HTML Block: (copy text below starting and ending with the 'script' tag)
/************************/
<script>
jQuery(function ($) {
    jQuery("#selectall").click(function() {
        jQuery(".check_email").prop("checked", this.checked);
    });
    jQuery(".selectedId").change(function() {
        var check = jQuery(".check_email").filter(":checked").length == jQuery(".check_email").length; 
        jQuery("#selectall").prop("checked", check);
    });
 jQuery('input[type=checkbox]').change(function() {
   // jQuery(".copy_emails").click(function() {
        var email_array = new Array();
        jQuery("input[name='emails']:checked").each(function() {
            email_array.push(jQuery(this).val());
        });
 
        var emails = email_array;
        var unique_emails = [];
        jQuery.each(emails, function(i, el){
            if(jQuery.inArray(el, unique_emails) === -1) unique_emails.push(el);
        });
        var text = jQuery('#input_7_1');//Change '7' to your form ID and '1' to the field ID that will hold the array of emails
        text.val(unique_emails);  
    });
});
</script>
/************************/
***ADD TO GRAVITYVIEW CUSTOM CONTENT FIELD***
<input class="check_email" type="checkbox" value="{email:3}" name="emails" > {email:3} // replace'{email:3} with the merge tag of your email field