Columns added at run-time didn't have the editor-
  plugin set and led to a JavaScript error

  - Disabling sorting by various columns because that confuses the Gantt display
  - Now allowing to edit all fields of super-tasks, except:
    - estimated_units
    - % done
    Before it was the other way around, only project_name was editable

  Now resizing the surface when maximizing the Gantt Editor

  - Added stateIds in order to fix stateful issue
  - Added stores for material, costcenter and status
  - Fixed stores

  even if the user didn't press the "Update" button.

  Now showing an error when unable to parse assignment

  - Restores defaults when clicking "reset configuration"
  - Fires the click(btn) event when resetting

  Finally fixed milestone_p issue(?)

  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.

  A milestone now is a task marked as milestone.
  It's not sufficient anymore to have start_date == end_date.
  That's because both date and timestamptz is used in the
  code on the DB and in the GanttEditor part.
  We will have to revisit this code once timephased_date are
  available in ]po[ V5.1 or later

  - Added CostCenter field
  - Added CostCenter model and store

  - Added read-only functionality and warnings