API cleanup, get rid of JsObject and GetProperty() methods that don`t return JsValue

shell/src/SubscriptionsCommand.cpp

 #include <iostream>
 #include <sstream>
 
 #include "SubscriptionsCommand.h"
 
 namespace
 {
   typedef std::vector<AdblockPlus::SubscriptionPtr> SubscriptionList;
 
   void ShowSubscriptionList(const SubscriptionList& subscriptions)
   {
     for (SubscriptionList::const_iterator it = subscriptions.begin();
          it != subscriptions.end(); it++)
     {
-      std::cout << (*it)->GetProperty("title", "(no title)") << " - " << (*it)->GetProperty("url", "");
-      if ((*it)->GetProperty("author", "") != "")
-        std::cout << " - " << (*it)->GetProperty("author", "");
-      if ((*it)->GetProperty("specialization", "") != "")
-        std::cout << " - " << (*it)->GetProperty("specialization", "");
+      std::cout << (*it)->GetProperty("title")->AsString();
+      std::cout << " - " << (*it)->GetProperty("url")->AsString();
+      if (!(*it)->GetProperty("author")->IsUndefined())
+        std::cout << " - " << (*it)->GetProperty("author")->AsString();
+      if (!(*it)->GetProperty("specialization")->IsUndefined())
+        std::cout << " - " << (*it)->GetProperty("specialization")->AsString();
       std::cout << std::endl;
     }
   }
 }
 
 SubscriptionsCommand::SubscriptionsCommand(
   AdblockPlus::FilterEngine& filterEngine)
   : Command("subscriptions"), filterEngine(filterEngine)
 {
 }
@@ skipping 77 matching lines @@
   const SubscriptionList& subscriptions = filterEngine.GetListedSubscriptions();
   for (SubscriptionList::const_iterator it = subscriptions.begin();
        it != subscriptions.end(); it++)
     (*it)->UpdateFilters();
 }
 
 void SubscriptionsCommand::FetchSubscriptions()
 {
   ShowSubscriptionList(filterEngine.FetchAvailableSubscriptions());
 }