Projects Sheet: Tasks

New entity `project_task`:
* project_id
* status (pending | done)
* created_by
* created_date
* title
* description?
* link?: { url, text }
* personnel_id (assigned team member)

> Who is the default person in charge of completing tasks? Isn't it the author/coauthor? Are author/coauthors personnel too?

Author, co-authors or auditors can mark tasks as completed

> Can Project personnel create new tasks? What role can create tasks?

I'd say only Auditors can create tasks

> Are tasks editable or deletable? Looks like it is missing from the design

They should, by the Auditors.