improve exit graph dialog

[capital-G]

Closes #489

Also displays when closing with unsaved changes

and w/o unsaved changes

[github-actions]

File	Coverage
All files	82%	✅
gencaster/distributor.py	69%	✅
gencaster/schema.py	67%	✅
gencaster/urls.py	77%	✅
osc_server/models.py	91%	✅
osc_server/server.py	55%	✅
story_graph/engine.py	74%	✅
story_graph/markdown_parser.py	85%	✅
story_graph/models.py	98%	✅
story_graph/types.py	99%	✅
stream/frontend_types.py	94%	✅
stream/models.py	91%	✅
stream/types.py	98%	✅

Minimum allowed coverage is 50%

Generated by 🐒 cobertura-action against 2bc4122

[vin-ni]

@capital-G fixed all the errors. ready to merge