Changes

Summary

1. updated to jdk-8u112;
2. basic SSH server configuration;
3. proper isabelle tool in Scala;
4. tuned;
5. merged
6. added system option "profiling";
7. replaced inefficient valid_accesses by is_valid_access, based on stored input accesses: e.g. relevant for Proof_Context.update_thms;
8. tuned signature, in accordance to Isabelle_System;
9. tuned;
10. clarified modules;
11. another attempt to squeeze a list into a property list entry;
12. report actual build_args;
13. more flexible multicore configuration;
14. clarified multiple props: result needs to fit on a single line within the log file;
15. clarified properties;
16. tuned;
17. support for free-form build tags; tuned;
18. explicit identification of builds and correlated build groups;
19. avoid spamming log file;
20. shared_home is default for classic isatest home setup; distinct ISABELLE_IDENTIFIER for all tasks;