file based provisioning + authentication support in add repo Intents

This merge request makes it possible to add HTTP-Basic-Auth enabled repositories via Intent. Using user-info part of a regular URL. (Intent-data example: https://user:pass@example.com/fdroid/repo)

The second feature in this MR is adding repositories from provisioning files. The client will now search for new provisions in {{externalFilesDir}}/provisions. Provisions are a zipped JSON-files with the file extension .fdrp. When F-Droid finds, provisions users will be prompted with our default dialog for adding repositories. All detected provision-files will be deleted after displaying them, regardless of weather the user applied them or not. The provision lookup only runs on App start (App.onCreate()).

(Note: This is intended for helping device vendors with provisioning F-Droid.)