Not updating start- and end date if they are null

  - Now uses im_project_nuke, so we don't have to maintain
    nuking code twice
  - Checks for timesheet hours and cost items before nuking

   User should get detailed view when clicking on Logged (Lg) in portlet "Timesheet Tasks" of page "/intranet/projects/view"

  - Moved main audit_impl into intranet-core
  - Replaced im_project_audit by im_audit