models: Use namespace std for std::size_t

model/syncthingdevicemodel.cpp

@@ -5,6 +5,7 @@
 #include "../connector/syncthingconnection.h"
 #include "../connector/utils.h"
 
+using namespace std;
 using namespace ChronoUtilities;
 
 namespace Data {

model/syncthingdirectorymodel.cpp

@@ -9,6 +9,7 @@
 
 #include <QStringBuilder>
 
+using namespace std;
 using namespace ChronoUtilities;
 using namespace ConversionUtilities;
 

model/syncthingdownloadmodel.cpp

@@ -5,6 +5,7 @@
 
 #include <QStringBuilder>
 
+using namespace std;
 using namespace ChronoUtilities;
 
 namespace Data {