2 bugfixes for image loading

[manuel-84]

first, encode the src because filenames with strange characters are not displayed during slider animation:

imgParam.backgroundImage = 'url(' + encodeURI($item.find( 'img' ).attr('src')) + ')';

second, setting the real size of image when all images are loaded

                // get real size of image
                var i = new Image();
                i.src = $current.find( 'img' ).attr( 'src' );
                i.onload = function() {
                    self.$el.css( {
                        'max-width' : this.width
                    } );
                }