Since I am striving for closer connection between my task management, my
mail suite and my calendar appointments, it makes sense to unify all
'office' tasks into the single office module instead of keeping
taskwarrior outside of it.
Added simple script `task-overdue-prompt` which checks for overdue tasks
(*not* tasks to be done 'today') and display a skull if there are any.
Intended for prompt use, it is currently still too slow to be used as
such. But there may still be uses other than that so it is included for now.