wui: fixed errors when serving taskdoc.html?fqtn=unknown.task.id
wui: enhanced request form field html display
config: avoid reimplemnting QString::join() by hand
config: subtasks named "subtask" instead of "task" and several improvements

main improvemnts:
- more work on config canonical pf writing (and thus hash id)
- more workflow config inconsistency warnings
config: requestform field: id as content and only one appendcommand

plus, now request form is part of task's canonical pf form