introduce query filter for REST API

Enabled WP REST API to query for ticker slug, GMT timestamp and limit
parameter as used by AJAX calls. This is done in preparation for
migration to WP REST instead of WP AJAX.

stklcode-liveticker.php

@@ -9,7 +9,7 @@
  * @wordpress-plugin
  * Plugin Name: Liveticker (by stklcode)
  * Description: A simple Liveticker for WordPress.
- * Version:     1.1.1
+ * Version:     1.2.0-alpha
  * Author:      Stefan Kalscheuer
  * Author URI:  https://www.stklcode.de
  * Text Domain: stklcode-liveticker
@@ -72,6 +72,7 @@ function scliveticker_autoload( $class ) {
 	$plugin_classes = array(
 		'SCLiveticker\\SCLiveticker',
 		'SCLiveticker\\Admin',
+		'SCLiveticker\\Api',
 		'SCLiveticker\\System',
 		'SCLiveticker\\Widget',
 	);