Check permissions for unattended installer
This PR introduces the class ``ApkVerifier`` which checks the permissions of the downloaded apk file against the expected permissions from the F-Droid listing (``Apk`` class).
* I removed ``AndroidXMLDecompress`` because everything which it has been used for can also be done with ``PackageManager.getPackageArchiveInfo()``, to the best of my knowledge. I even asked in at a similar project why ``PackageManager.getPackageArchiveInfo()``may not be enough: https://github.com/jaredrummler/APKParser/issues/3 It turns out in our case it should do everything we need.
* The code responsible for sanitizing the local apk file and making it world readable has also been moved into ``ApkVerifier`` for now. This can change in a later PR when I introduce the FileProvider for downloaded apks.
We still need to check the target sdk version (see TODO in ``ApkVerifier``). This depends on https://gitlab.com/fdroid/fdroidclient/merge_requests/323
See merge request !322
7e27edc9b5