Open protection level of OSObservable for testing

Added to OneSignalPackagePrivateHelper.java to allow for direct testing
of this class without making it a public class to the released SDK.

Author: jkasten2

OneSignalSDK/unittest/src/test/java/com/onesignal/OneSignalPackagePrivateHelper.java

@@ -824,4 +824,18 @@ public OSNotification build() {
          }
       }
    }
+
+   public static class OSObservable<ObserverType, StateType> extends com.onesignal.OSObservable<ObserverType, StateType> {
+      public OSObservable(String methodName, boolean fireOnMainThread) {
+         super(methodName, fireOnMainThread);
+      }
+
+      public void addObserver(ObserverType observer) {
+         super.addObserver(observer);
+      }
+
+      public void removeObserver(ObserverType observer) {
+         super.removeObserver(observer);
+      }
+   }
 }