Add task description as cost name

[k4ffee]

Hello,
I created an option which uses the task description instead of the <task_id>_<user_id> variant for the costs name field. The default behavior stays unchanged, it is configurable. On task completion automatically add a costs entry with task description as costs name. If the description is longer than 255 chars, it will be cut and ... appended.

If you are fine with this, I would make a PR

Best regards
Michael