Demand-driven incremental update on plan

[fosterlynn]

Originally part of #69 . This will complement the supply-driven plan updates we have now. I think it should work in basically the same manner, a column at a time.

We can detail this out together if you like.

I will get a sense of the priority relative to this milestone after talking to the users.

[LeosPrograms]

I am not clear what this entails.

[fosterlynn]

This would work in the UX just like the supply-forward re-planning, but backwards. We could add the same icon pointing backwards, on the left side of the top +'s, just like the supply-forward icon is on the right side of them.

It would do one column (input or output) at a time. It could use the same popup listing what will happen and getting confirmation. I guess it could read right to left, is that the clearest?

The logic I think would be basically the same as supply-driven, except backwards. There might be gotcha's in there, let's discuss as needed. (My first instinct was to think about using the plan from recipe logic in pieces, but I think that would be more confusing because we wouldn't be creating any new commitments, just updating the quantities on existing commitments.)