Workboard Columns: avoid page reload on Edit > Cancel

Summary:
The rationale for this change is that reloading a page unnecessarily wastes
resources that we can save.

This includes human resources (time) but also computational resources
as well. We probably save a fawn for every 1,000 clicks on that button.
A message to Greta Thunberg: now Phorge is with you.

This is the involved "Cancel" button, that does not reload the page anymore:

{F309894}

Closes T15471

Test Plan:
Workboard > Column > Edit > Cancel:

The popup closes gracefully instead of a page refresh.

Also try opening the workflow in another tab (/project/board/1/hide/2/) > Cancel:

You turn back to your Workboard just as before.

Reviewers: O1 Blessed Committers, Matthew

Reviewed By: O1 Blessed Committers, Matthew

Subscribers: speck, tobiaswiese, Matthew, Cigaryno

Maniphest Tasks: T15471

Differential Revision: https://we.phorge.it/D25302