Extract app store link to a constant

Trust/Settings/Coordinators/HelpUsCoordinator.swift

@@ -31,7 +31,7 @@ class HelpUsCoordinator: Coordinator {
 
     func rateUs() {
         if #available(iOS 10.3, *) { SKStoreReviewController.requestReview() } else {
-            UIApplication.shared.openURL(URL(string: "itms-apps://itunes.apple.com/app/id1288339409")!)
+            UIApplication.shared.openURL(URL(string: Constants.appstoreURL)!)
         }
         appTracker.completedRating = true
     }

Trust/Settings/Types/Constants.swift

@@ -14,6 +14,8 @@ public struct Constants {
     public static let twitterUsername = "Alpha_wallet"
     public static let redditGroupName = "r/AlphaWallet/"
     public static let facebookUsername = "AlphaWallet"
+    //TODO need to change this for launch
+    public static let appstoreURL = "itms-apps://itunes.apple.com/app/id1288339409"
 
     // support
     public static let supportEmail = "support@awallet.io"