Add shadow behind the what's new pages

As discussed during the eCCB.

resources/qml/WelcomePages/WhatsNewContent.qml

@@ -4,6 +4,7 @@
 import QtQuick 2.10
 import QtQuick.Controls 2.3
 import QtQuick.Layouts 1.3
+import QtGraphicalEffects 1.12 // For the DropShadow
 
 import UM 1.3 as UM
 import Cura 1.1 as Cura
@@ -91,6 +92,13 @@ Item
                         source: manager.getSubpageImageSource(index)
                     }
 
+                    DropShadow {
+                        anchors.fill: subpageImage
+                        radius: UM.Theme.getSize("monitor_shadow_radius").width
+                        color: UM.Theme.getColor("first_run_shadow")
+                        source: subpageImage
+                    }
+
                     Cura.ScrollableTextArea
                     {
                         id: subpageText