Include <QAuthenticator> from code that connect to signal that uses it

The new connection syntax will need that

src/libsync/abstractnetworkjob.cpp

@@ -26,6 +26,7 @@
 #include <QTimer>
 #include <QMutex>
 #include <QCoreApplication>
+#include <QAuthenticator>
 
 #include "networkjobs.h"
 #include "account.h"

src/libsync/account.cpp

@@ -32,6 +32,7 @@
 #include <QFileInfo>
 #include <QDir>
 #include <QSslKey>
+#include <QAuthenticator>
 
 namespace OCC {
 

src/libsync/creds/httpcredentials.cpp

@@ -31,6 +31,7 @@
 #include "syncengine.h"
 #include "creds/credentialscommon.h"
 #include "creds/httpcredentials.h"
+#include <QAuthenticator>
 
 using namespace QKeychain;