Workboards - let users delete columns

Summary: Fixes T4408. I had to add a "status" to colum. I think we'll need this once we get fancier anyway but for now we have "active" and deleted.

Test Plan: deleted a column. noted reloaded workboard with all those tasks back in the default colun. loaded a task and saw the initial transaction had a "Disabled" icon next to the deleted workboard. also saw the new transaction back to the default column worked.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T4408

Differential Revision: https://secure.phabricator.com/D8544