Build and send a book only when it changed

A key of the chapters, rules and metadata of a story tells if its book
changed. A check without a change no longer builds the book again, also
for a book that waits for an upload. A held book goes out without a new
build. The Rebuild button still builds and sends in each case.

tests/test_deliver.py

@@ -60,7 +60,8 @@ def opf(name):
 
 
 def rebuild(story_id):
-    return orchestrator._run_rebuild(Job(mode=DownloadMode.REBUILD, story_id=story_id))
+    """A rebuild that the user asks for. It builds and sends the book also when the book did not change."""
+    return orchestrator._run_rebuild(Job(mode=DownloadMode.REBUILD, story_id=story_id, options={"force": True}))
 
 
 def test_first_version_goes_in_as_a_new_book(fake):