Task: Use dates instead of datetimes when setting fields in ActionSucceeded subscribers.

`expectedStartOfWork` and `date_of_completion` are Date fields, not DateTime.
And so are the corresponding columns in SQL.
Merge pull request #555 from 4teamwork/lg-use-dates-in-task-wf-change-subscribers

Task: Use dates instead of datetimes when setting fields in ActionSucceeded subscribers.