GH-903 force Dark theme to use Fusion Qt style

Themes now include Qt styles.

application/MultiMC.cpp

@@ -22,6 +22,7 @@
 #include <QMessageBox>
 #include <QStringList>
 #include <QDebug>
+#include <QStyleFactory>
 
 #include "InstanceList.h"
 #include <minecraft/auth/MojangAccountList.h>
@@ -982,9 +983,9 @@ void MultiMC::setApplicationTheme(const QString& name)
 	if(themeIter != m_themes.end())
 	{
 		auto & theme = (*themeIter).second;
+		setStyle(QStyleFactory::create(theme->qtTheme()));
 		setPalette(theme->colorScheme());
 		setStyleSheet(theme->appStyleSheet());
-		//setStyle(QStyleFactory::create("Fusion"));
 	}
 	else
 	{

application/themes/DarkTheme.cpp

@@ -10,6 +10,11 @@ QString DarkTheme::name()
 	return QObject::tr("Dark");
 }
 
+QString DarkTheme::qtTheme()
+{
+	return "Fusion";
+}
+
 QPalette DarkTheme::colorScheme()
 {
 	QPalette darkPalette;

application/themes/DarkTheme.h

@@ -7,6 +7,7 @@ class DarkTheme: public ITheme
 public:
 	virtual ~DarkTheme() {}
 
+	QString qtTheme() override;
 	QString id() override;
 	QString name() override;
 	QString appStyleSheet() override;

application/themes/ITheme.h

@@ -9,5 +9,6 @@ public:
 	virtual QString id() = 0;
 	virtual QString name() = 0;
 	virtual QString appStyleSheet() = 0;
+	virtual QString qtTheme() = 0;
 	virtual QPalette colorScheme() = 0;
 };

application/themes/SystemTheme.cpp

@@ -1,10 +1,26 @@
 #include "SystemTheme.h"
 #include <QApplication>
 #include <QStyle>
+#include <QStyleFactory>
+#include <QDebug>
 
 SystemTheme::SystemTheme()
 {
-	systemPalette = QApplication::style()->standardPalette();
+	const auto & style = QApplication::style();
+	systemPalette = style->standardPalette();
+	QString lowerThemeName = style->objectName();
+	qWarning() << systemTheme;
+	QStringList styles = QStyleFactory::keys();
+	for(auto &st: styles)
+	{
+		if(st.toLower() == lowerThemeName)
+		{
+			systemTheme = st;
+			return;
+		}
+	}
+	// fall back to fusion if we can't find the current theme.
+	systemTheme = "Fusion";
 }
 
 QString SystemTheme::id()
@@ -17,6 +33,11 @@ QString SystemTheme::name()
 	return QObject::tr("System");
 }
 
+QString SystemTheme::qtTheme()
+{
+	return systemTheme;
+}
+
 QPalette SystemTheme::colorScheme()
 {
 	return systemPalette;

application/themes/SystemTheme.h

@@ -10,6 +10,7 @@ public:
 
 	QString id() override;
 	QString name() override;
+	QString qtTheme() override;
 	QString appStyleSheet() override;
 	QPalette colorScheme() override;
 private: