Make Metadata functions static

Convert function (to manage MetaDataField to/from Int) has static

Author: jano42

cpp/src/Node.h

@@ -902,8 +902,8 @@ namespace OpenZWave
 					string description;
 			};
 			string const GetMetaData(MetaDataFields);
-			MetaDataFields GetMetaDataId(string);
-			string const GetMetaDataString(MetaDataFields);
+			static MetaDataFields GetMetaDataId(string);
+			static string const GetMetaDataString(MetaDataFields);
 			ChangeLogEntry const GetChangeLog(uint32_t);
 
 		private: