[IMP] project: task: added reviewer_id field, linking towards a res.users, that is the
reviewer of the task. This field is automatically tracked, using a small update of the get_auto_subscribe_fields method that is
weirdly implemented.
Merge pull request #464 from odoo-dev/master-task-reviewer-tde

[IMP] project: task: added reviewer_id field, linking towards a res.users, that is the reviewer of the task.