Add missing header includes to build against Qt 5.11.0

Some Qt gui headers are no longer included when including QtGui
adding these two missing headers makes Synergy build here on windows.

src/gui/src/ActionDialog.cpp

@@ -26,6 +26,8 @@
 #include <QtCore>
 #include <QtGui>
 
+#include <QButtonGroup>
+
 ActionDialog::ActionDialog(QWidget* parent, ServerConfig& config, Hotkey& hotkey, Action& action) :
     QDialog(parent, Qt::WindowTitleHint | Qt::WindowSystemMenuHint),
     Ui::ActionDialogBase(),

src/gui/src/ScreenSetupView.cpp

@@ -23,6 +23,8 @@
 #include <QtCore>
 #include <QtGui>
 
+#include <QHeaderView>
+
 ScreenSetupView::ScreenSetupView(QWidget* parent) :
     QTableView(parent)
 {