configure_input: Hook up the motion button and checkbox

This allows toggling motion on or off, and allows access to the motion configuration.
Also changes the [waiting] text for motion buttons to Shake! as this is how motion is connected to a player.

src/core/settings.h

@@ -152,6 +152,7 @@ struct Values {
 
     bool vibration_enabled;
 
+    bool motion_enabled;
     std::string motion_device;
     std::string touch_device;
     TouchscreenInput touchscreen;