Fixed "GanttEditor: Error saving data on the server side: No authentication found ('')" bug.
  Apparently Chrome sometimes sends out PUT XHTTP calls without cookies.
  So ]po[ then correctly identifies a non-authenticated session.
  As a workaround, I have added auth_token authentication in the SenchaPreference store,
  so that the calls are authenticated, even if the cookies should disappear for some
  reason.

  - Added CostCenter field
  - Added CostCenter model and store

  - Improved error message
  - Added remaining columns to GanttTreeStore (material)

  suitable to be parsed by Sencha ExtJS

  - Added permissions to POST on im_hours

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

  indicating the type of object (task, project, ticket, ...)

  Fixed issue deleting assignations

  Fixed issue saving Gantt Editor task trees with dependencies:
  Now dependencies are saved in a second "pass"

  Now CRUD for timesheet_task dependencies stored
  as part of the Sencha tree store