
Fixes #625, as devices pre 4.0 require such `PendingIntent`s to be passed to the notificaitons `setContentIntent` method. As the `DownloaderService` handles both apks and repo updates, the pending intent will either point to the relevant `AppDetails` screen for an apk download - or the main F-Droid activity if it is any other sort of download (i.e. a repo update download).