implement 3 configurable and toggleable framerate targets (#2159)

This pr allows for configuring the framerate target and adds support for two other framerate targets, a "fastforward" and "slowmo" target which can be enabled via either a toggle or holding a button.
this allows for supporting a more accurate framerate target and allows for users to slow down the speed of gameplay if they so desire

src/frontend/qt_sdl/InterfaceSettingsDialog.h

@@ -60,6 +60,16 @@ private slots:
 
     void on_cbMouseHide_clicked();
 
+    void on_pbClean_clicked();
+    void on_pbAccurate_clicked();
+
+    void on_pb2x_clicked();
+    void on_pb3x_clicked();
+    void on_pbMAX_clicked();
+
+    void on_pbHalf_clicked();
+    void on_pbQuarter_clicked();
+
 private:
     Ui::InterfaceSettingsDialog* ui;