Add migration wizard, fix migration from custom paste instance

- Very basic wizard just to allow the user to choose whether to keep
  their old paste settings or use the new default settings.

- People who used custom 0x0 instances would just be kept on those
  settings and won't see the wizard.

launcher/ui/setupwizard/PasteWizardPage.h

@@ -0,0 +1,27 @@
+#ifndef PASTEDEFAULTSCONFIRMATIONWIZARD_H
+#define PASTEDEFAULTSCONFIRMATIONWIZARD_H
+
+#include <QWidget>
+#include "BaseWizardPage.h"
+
+namespace Ui {
+class PasteWizardPage;
+}
+
+class PasteWizardPage : public BaseWizardPage
+{
+    Q_OBJECT
+
+public:
+    explicit PasteWizardPage(QWidget *parent = nullptr);
+    ~PasteWizardPage();
+
+    void initializePage() override;
+    bool validatePage() override;
+    void retranslate() override;
+
+private:
+    Ui::PasteWizardPage *ui;
+};
+
+#endif // PASTEDEFAULTSCONFIRMATIONWIZARD_H