compatibility with query string images for video detection upgrade. (fix included)

[HawkenKing]

If you are detecting images or videos and an image is loaded with a query string, for example in wordpress with a plugin, the lightbox can default to a video iframe if your code is augmented to run videos.

Here is a fix to keep images from turning into iframes when they have a query string url:

SlickLightbox.prototype.detectImage = function(url) {
    // Remove query string 
    url = url.split('?')[0];

    // Returns true if it finds an image file extension
    return url.match(/\.(jpeg|jpg|gif|png|webp)$/i) !== null;
};

Also added support for webp.