add looping for slides

This add looping primarily for videos but I've added in the groundwork
for looping through any kind of slide. This obviously will be
implemented differently for each type of slide, but this way the
groundwork is done already.

src/main.cpp

@@ -169,7 +169,7 @@ int main(int argc, char *argv[])
     serviceItemModel.get()->addItem("Black", "image",
                                     "qrc:/assets/black.jpg",
                                     "image", QStringList(""),
-                                    "", "", 0, 1);
+                                    "", "", 0, 1, false);
   }
 
   // apparently mpv needs this class set