Fix build with Qt 5.11 (#6029)

src/playlist/playlistcontainer.cpp

@@ -23,6 +23,7 @@
 #include "playlistparsers/playlistparser.h"
 #include "ui/iconloader.h"
 
+#include <QAction>
 #include <QFileDialog>
 #include <QInputDialog>
 #include <QKeyEvent>

src/ui/globalshortcutssettingspage.cpp

@@ -24,6 +24,7 @@
 #include "ui/iconloader.h"
 #include "ui/settingsdialog.h"
 
+#include <QAction>
 #include <QKeyEvent>
 #include <QMessageBox>
 #include <QProcess>

src/widgets/errordialog.cpp

@@ -18,6 +18,8 @@
 #include "errordialog.h"
 #include "ui_errordialog.h"
 
+#include <QStyle>
+
 ErrorDialog::ErrorDialog(QWidget* parent)
     : QDialog(parent), ui_(new Ui_ErrorDialog) {
   ui_->setupUi(this);