Ref T13513. Currently, if you:

• click a line to create an inline;
• type some text;
• wait a moment; and
• close the page.

...you don't get an "Unsubmitted Draft" marker in the revision list.

Lift all the draft behavior to "InlineController" and make saving a draft dirty the overall container draft state.

• Took the steps described above, got a draft state marker.
• Created, edited, submitted, etc., inlines in Diffusion and Differential.