replace binaries and aubio source files by a build script

[piem]

Most files in the jni folder should be generated by a script from the latest stable release of aubio, instead of being shipped directly in the repository.

Less important, but would also be nice: stock images found in app/src/main/res are also not really relevant to this repository and should be fetched or created automatically.

In general, files that are generated should not go in a git repository, and they should be replaced by a script to create them.