Add "move cell to section" feature

[anjiro]

Description

Rearranging cells in a large notebook is rather difficult, especially if there is a lot of complex output (e.g., DataFrames or plots) which slow down dragging cells around. It would be nice to have an easier way of moving things.

Suggested solution

In addition to the "Move Cell Up/Down" and "Send Cell to Top/Bottom" menu items, being able to move a cell to a Markdown-headed section would be very convenient.

Alternative

No response

Additional context

No response

[akshayka]

When I need to move a lot of cells around, I end up doing it in a text editor instead of the marimo editor. Thought that does require shutting down your notebook first.

[anjiro]

Yeah, I've thought of that, but in cases where I have a lot of cells I need to navigate around, then I really don't want to shut down and have to re-run (often it's lots of plots which take a good while to generate and aren't amenable to memoizing).