Hey look i have created test to show you how to do this
See Blocks :
Download aia :
Showing download in app not in notification.aia (306.9 KB)
Download apk :
Showing download in app not in notification.apk (5.5 MB)
Extensions Used :
ExtendedDownloader Extension [FREE]
Circular Progress Extension (Preview)
CustomWebView : An extended form of Web Viewer
hope this helped you 
Reply if you have any problems