CC-2756: Ability to set plan level

- created setter and getter in Preference.php for plan level
- renamed airtime-stream to airtime-system
- airtime-system is removed from this repository(moved to airtime-saas)

airtime_mvc/application/models/Preference.php

@@ -410,5 +410,13 @@ class Application_Model_Preference
     public static function GetMaxBitrate(){
         return Application_Model_Preference::GetValue("max_bitrate");
     }
+    
+    public static function SetPlanLevel($plan){
+        Application_Model_Preference::SetValue("plan_level", $plan);
+    }
+    
+    public static function GetPlanLevel(){
+        return Application_Model_Preference::GetValue("plan_level");
+    }
 }