Send out PROVIDER_CHANGED broadcasts again, fixes #822 (#825)

Since Android 8 it's not possible to listen to implicit broadcasts anymore when the reciever is declared in the AndroidManifest.xml.
In a previous commit we disabled sending out broadcasts to other apps. This caused some trouble.
For new we hard code 3rd party receiver package names in a resource array. This is supposed to be changed later on, see #824.