Improved support for Android apk files

Android packages/apps (.apk) are Java archvies, which were
already handled by diffoscope to a certain extent.
The collection of class files (classes.dex) was already converted
by enjarify to proper class files.
But there are additional important files like the AndroidManifest.xml
(which is a binary XML format) and resources.arsc. Those are now also
properly diffable by using apktool for dumping the apk contents.