Add custom class to attendees URLs (#1381)

This mimics what happens for other questions where a class `tix-question-name` is added, allowing for further styling.
Currently URLs only get the same, generic classes making it very difficult to style them according to their nature.

public_html/wp-content/plugins/camptix/addons/field-url.php

@@ -75,7 +75,7 @@ function attendees_shortcode_item( $attendee_id ) {
 					$label = substr( $label, 4 );
 				}
 
-				printf( '<a class="tix-field tix-attendee-url" href="%s">%s</a>', esc_url( $url ), esc_html( $label ) );
+				printf( '<a class="tix-field tix-attendee-url tix-%s" href="%s">%s</a>', esc_attr( $question->post_name ), esc_url( $url ), esc_html( $label ) );
 			}
 		}
 	}