basic implementation of having reveal.js slides working

There is still a lot of work needed to be done here, but the basics
are laid out.

src/qml/presenter/PreviewSlideListDelegate.qml

@@ -1,6 +1,7 @@
 import QtQuick 2.15
 import QtQuick.Controls 2.15 as Controls
 import QtQuick.Layouts 1.15
+import QtWebEngine 1.10
 import org.kde.kirigami 2.13 as Kirigami
 import "./" as Presenter
 import org.presenter 1.0
@@ -36,12 +37,27 @@ Item {
             implicitHeight: parent.height - Kirigami.Units.smallSpacing * 2
             textSize: model.fontSize
             itemType: model.type
-            imageSource: model.videoBackground != "" ? model.videoThumbnail : model.imageBackground
+            imageSource: {
+                if (model.videoBackground != "") {
+                    return model.videoThumbnail;
+                } else if (model.imageBackground.endsWith(".html")) {
+                    return "";
+                } else
+                    return model.imageBackground;
+            }
             chosenFont: model.font
             text: model.text
             pdfIndex: model.slideIndex
 
         }
+        WebEngineView {
+            id: web
+            anchors.centerIn: parent
+            implicitWidth: height / 9 * 16
+            implicitHeight: parent.height - Kirigami.Units.smallSpacing * 2
+            url: model.imageBackground.endsWith(".html") ? model.imageBackground : ""
+            visible: model.imageBackground.endsWith(".html")
+        }
     }
 
     Controls.Label {