Android Java bindings generation

This adds a script which reads Owr-1.0.gir and generates Java classes along with the corresponding JNI implementation.

I also modified the build to create .jar files for the libraries and Java classes. This is quite ugly at the moment, since autotools + Java = :broken_heart:. At the moment it's just done at the end of build.sh, would it e.g. be better to add it as a `make install` target?

The python code is also quite ugly, I'll refactor it at some point, but for now I think it's better to be able to provide some useful way to use Owr on Android.