QmlDesigner: Add files for testing image formats

tests/manual/qml/testfiles/images.qml

+import Qt 4.6
+
+Rectangle {
+    width: 640
+    height: 480
+
+    Image {
+        id: image1
+        x: 20
+        y: 18
+        source: "images/qtcreator.png"
+    }
+
+    Image {
+        id: image2
+        x: 327
+        y: 18
+        source: "images/qtcreator.jpg"
+    }
+
+    Image {
+        id: image3
+        x: 20
+        y: 288
+        source: "images/qtcreator.ico"
+    }
+}