revealJS presentations work sorta

I still have lots of bugs, but the groundwork is there. At least a
proof of concept.

src/qml/presenter/PresentationWindow.qml

@@ -107,4 +107,12 @@ Item {
     function loopVideo() {
         presentationSlide.loopVideo();
     }
+
+    function revealNext() {
+        presentationSlide.revealNext();
+    }
+
+    function revealPrev() {
+        presentationSlide.revealPrev();
+    }
 }