Fixed jQuery form.submit event handling

Ladda overrides jQuery form handlers by disabling button before form's `submit` event fires. Consider following code:

    <form id="form" action="/wrong/url">
        <button type="submit" class="ladda-button" data-style="zoom-in">
            <span class="ladda-label">Submit</span>
            <span class="ladda-spinner"></span>
        </button>
    </form>
    
    <script>
        $(function() {
            Ladda.bind('.ladda-button');
        }
        
        $(function() {            
            $('#form').submit(function() {
                alert('submitted');
                return false;
            })
        });
    </script>

And here is a live example: http://poma.su/ladda

After clicking button user will be redirected to `/wrong/url` instead of alert shown.