Changes

Summary

1. synchronous use_theories, based on consolidated_state;
2. clarified modules;
3. optional session_base, e.g. from existing Sessions.Deps in build.scala;
4. synchronous session start (similar to isabelle.vscode.Server);
5. tuned signature (again, see 1a9e2a2bf251);
6. tuned signature;
7. simplified: eliminated pointless Thy_Document_Model;
8. theory nodes are never visible: avoid prints, which are not covered by node_consolidated;
9. load theories via PIDE document update; theory nodes are always required;
10. tuned signature;
11. PIDE resources for theory files;
12. tuned;
13. tuned signature;