lots of new material, ultimately related to measure theory

merged

support for lazy notes in global/local context and Element.Lazy_Notes: name binding and fact without attributes; register_proofs is now based on lazy thms, but Thm.consolidate_theory will eventually force this (in parallel); support for lazy notes for locale activation (still inactive);

tuned;

tuned: more parallel;

clarified modules;

clarified modules;

tuned;

tuned;

tuned signature;

tuned: more accurate transfer;

store facts as lazy values;

clarified operations;

misc tuning and clarification;

clarified signature;