Add a hook to filter gallery classes

[grosbouff]

Hi, it would be really great to be allowed to filter the gallery classes.

Here's what I suggest :

instead of :

	$size_class = sanitize_html_class( $atts['size'] );
	$gallery_div = "<div id='$selector' class='gallery galleryid-{$id} gallery-columns-{$columns} gallery-size-{$size_class}'>";

rather use

        $classes_str = null;
        $classes = array(
            'gallery',
            'galleryid-'.$id,
            'gallery-columns-'.$columns,
            'gallery-size-'.sanitize_html_class( $atts['size'] )
        );
        
        $classes = apply_filters('gallery_classes',$classes,$attr);

        if (!empty($classes)){
            $classes = array_filter($classes);
            $classes_str = " class='".implode(' ',$classes)."'";
        }
        

	$size_class = sanitize_html_class( $atts['size'] );
	$gallery_div = "<div id='$selector' $classes_str>";

[mahype]

Added actionhook like in example above.

[desrosj]

29379.diff​ needs to be refreshed against the current code base.

While gallery blocks are the preferred way to implement galleries now and they do not use gallery_shortcode() directly, I think this is a reasonable change to make. Adding a classes attribute to $attr may also make sense to accompany this.

[shailu25]

Refreshed Patch.