Changes

Summary

1. clarified signature: more explicit types;
2. more robust: prefer internal theory names;
3. clarified session_sources (again, see also 9d0e6ea7aa68);
4. clarified signature: more explicit types;
5. tuned output;
6. clarified signature: more general operations;
7. clarified signature: more explicit types;
8. clarified signature: more explicit types (see also 90c552d28d36);
9. do write_session_sources early, to have information available in build job;
10. tuned signature, following Url.append_path;
11. do not bundle Isabelle/Naproche, while it keeps changing;
12. tuned signature;
13. tuned;
14. clarified signature: uniform master_dir instead of separate field;
15. more standard master_dir;