AKModel: Fix default state of plan_hidden in new event wizard

Currently, plan_hidden is always false -- which cannot be changed through the event creation wizard since the field is hidden. Oh the irony...

added bug label

changed the description

changed milestone to %KIF 50,5

mentioned in commit 96cfbc37

mentioned in commit 40ce509c

closed with commit 40ce509c

mentioned in commit e1cebf37