Workflow to prevent deletion or removal of last PI

[Republicof1]

A refined workflow of modals to support management of investigators on proposal

[AllanEngland]

Looks good to me, but you'll want to fix the (minor) build issues before merging:

Error: src/ProposalEditorView/investigators/List.tsx(1,10): error TS6133: 'Children' is declared but its value is never read.
Error: src/ProposalEditorView/investigators/List.tsx(24,1): error TS6133: 'forEach' is declared but its value is never read.

[DJWalker42]

This is personal opinion but I prefer simply disabling a button when you want to prevent someone from doing something, and providing an alternate tooltip to explain why the button is disabled. Having the button enabled then popping up an alert when it is pressed and the "prevention" condition is met, may feel jarring for the user; "if you knew I couldn't do that why was the button enabled?".

That being said, this does do what it says on the tin. Also, as Allan wrote, those build issues need fixing (very minor i.e., remove the unused imports ).