Changes

Summary

1. session directories need to exist;
2. clarified signature: eliminated unused option;
3. merged
4. importation fix
5. merged
6. new material on Analysis, plus some rearrangements
7. eliminated pointless theory graph (reverting parts of a56eab490f4e): it caused problems with loaded vs. non-loaded node names, e.g. for theory Pure (see also 29bb1ebb188f);
8. discontinued obsolete "isabelle imports" and all_known data;
9. avoid duplicate directories wrt. synthetic session;
10. disallow accidental duplicates within the same session specification -- proper total match;
11. find theory files via session structure: much faster Prover IDE startup;