GH-992 Add a transaction/locking mechanism to settings objects

This can cut the FTB loading by ~66% - worth it, but not ideal.
Real solution will have to be implemented later.

application/pages/InstanceSettingsPage.cpp

@@ -14,7 +14,7 @@
 InstanceSettingsPage::InstanceSettingsPage(BaseInstance *inst, QWidget *parent)
 	: QWidget(parent), ui(new Ui::InstanceSettingsPage), m_instance(inst)
 {
-	m_settings = &(inst->settings());
+	m_settings = inst->settings();
 	ui->setupUi(this);
 	loadSettings();
 }

application/pages/InstanceSettingsPage.h

@@ -69,6 +69,6 @@ private slots:
 private:
 	Ui::InstanceSettingsPage *ui;
 	BaseInstance *m_instance;
-	SettingsObject *m_settings;
+	SettingsObjectPtr m_settings;
 	QObjectPtr<JavaCommon::TestCheck> checker;
 };