Changes

Summary

1. enforce rebuild of Isabelle/ML;
2. more direct state update;
3. avoid too many synchronized_database;
4. tuned output;
5. synchronize progress messages with database;
6. more robust SQL query for mandatory arguments;
7. synchronize progress stop/stopped with database;
8. more database content;
9. tuned whitespace;
10. tuned signature;
11. tuned whitespace;
12. clarified signature: avoid confusion due to object-orientation;
13. clarified modules;
14. clarified signature: prefer explicit types;
15. more accurate Sessions.Info.session_prefs: cover relative changes wrt. statically declared options;
16. clarified signature: more explicit type Options.Spec, which incorporates all variants of Options.+;
17. tuned output;
18. clarified signature: more explicit types;
19. clarified signature: prefer static types;
20. clarified signature (again, see also 8c64e51d9dde and 268bf61631ec);
21. tuned signature;