See mockup: https://s.codepen.io/enalean/debug/615728ad14def79e9b694647c582ce16
At this step, I can expand and collapse columns. Contrary to what the mockup is showing, the column width must be "slim" (like Kanban).
As introduced in story #13730, we will pass JSON information describing the taskboard columns to the app. The JSON information should contain the "collapsed / expanded" state for columns, so that the columns appear collapsed or expanded directly (without flicker).
Collapsed column information is stored as a user preference.