title: How to check if an extention is installed
body: <p>We offer multiple iMessage extensions. Example ExtensionA and ExtensionB. </p>
  
  <p>ExtensionB offers InApp purchases InAppPurchaseA and InAppPurchaseB. </p>
  
  <p>InAppPurchaseA should be free, if ExtensionA is installed on the device.</p>
  
  <p>How to check if ExtensionA is installed?</p>