Android: Support installing .obbs outside of .xapks

[baltpeter]

#64 brings support for installing .xapk files, including any .obb files they may contain.

But .obbs also occur outside of .xapks. For example, PlaystoreDownloader also supported downloading these with the -b flag.

We need to support passing them to installApp() along the split APKs. Shouldn't be hard now that we already have support for installing them.

[baltpeter]

Interestingly, the PlaystoreDownloader linked to https://android-developers.googleblog.com/2020/11/new-android-app-bundle-and-target-api.html. Apparently, .obbs are now deprecated. We should still support them for the time being now that @zner0L has implemented support anyway.