R1:9bca1a56da65

Begin generalizing Javascript for Workboard state handling

Summary:
Ref T4900. Broadly, workboard state management is fairly ad-hoc now, which makes things like this (where some kind of edit affects global state) difficult:

- Updating points header to reflect a sum change after dragging a task.
- Changing progress bars after editing a task to change resolution or points value.
- Moving a card to the correct column after editing it and changing subprojects/iterations.
- Responding to real-time…