Make our fetch-gradle-dependencies script smarter regarding dependency location

We fetch gradle dependencies with our fetch-gradle-dependencies script but don't really care where exactly we put them in that process. We should change that, though, because otherwise we need to do things like cp -r $gradle_repo/m2/* $gradle_repo in build scripts to adjust the paths so that gradle can find them.

That's a thing our script should do in the first place to avoid complexity in our build scripts.