Move System Applets into a new category and deselect by default

As they are known to cause problems with Mii Maker and games like Tomodachi Life.

src/frontend/import_dialog.h

@@ -64,7 +64,9 @@ private:
     bool program_trigger = false;
 
     // Whether the System Archive / System Data warning has been shown
-    bool warning_shown = false;
+    bool system_warning_shown = false;
+    // Whether the Applets warning has been shown
+    bool applet_warning_shown = false;
 
     // TODO: Why this won't work as locals?
     Core::ContentSpecifier current_content = {};