Added partial onChange callback (with only String key) for back-compat and simplicity

Author: gilmaimon

src/CloudStorage.h

@@ -9,6 +9,8 @@
 #include <functional>
 
 typedef std::function<void(String, AnyValue&)> KeyChangedCallback;
+typedef std::function<void(String)> KeyChangedCallbackPartial;
+
 enum PopFrom {
   PopFrom_Start,
   PopFrom_End
@@ -46,6 +48,12 @@ class BaseCloudStorage {
   void onChange(KeyChangedCallback callback) {
     this->_listenCallback = callback;
   }
+  
+  void onChange(KeyChangedCallbackPartial callback) {
+    this->_listenCallback = [&callback](String key, AnyValue& value){
+      callback(key);
+    };
+  }
 
   bool isListeningForUpdates() {
     return client.available() && this->_connectionState == WS_STATE_CONNECTED;