QtQuickPrototype wizard: Set example importPaths to "asset_imports"

"asset_imports" is the default subpath where the QmlDesigner resource
importer will create QML modules with imported 3d assets.

Facitiltate the inclusion of these assets by having the asset_imports
directory as example importPath.

Change-Id: I6977ff2f2cc1c6d34f5def005bfef99313021ee7
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

share/qtcreator/templates/wizards/projects/qtquickuiprototype/app.qmlproject

@@ -16,5 +16,5 @@ Project {
         directory: "."
     }
     /* List of plugin directories passed to QML runtime */
-    // importPaths: [ "../exampleplugin" ]
+    // importPaths: [ "asset_imports" ]
 }