support mod_vad_detect (#762)

* support mod_vad_detect

* wip

* update verb spec and drachtio fsmrf

* Update example-voicemail-greetings.json (#761)

Update voicemail english greetings

* wip

* stopvad if playdone

---------

Co-authored-by: Vinod Dharashive <vdharashive@gmail.com>

lib/session/call-session.js

@@ -338,6 +338,17 @@ class CallSession extends Emitter {
     this.application.fallback_speech_recognizer_language = language;
   }
 
+  /**
+   * Vad
+   */
+  get vad() {
+    return this._vad;
+  }
+
+  set vad(v) {
+    this._vad = v;
+  }
+
   /**
    * indicates whether the call currently in progress
    */