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

  - Added material as a column

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

  - Moved MS-Project Warning portlet to the bottom of the project page
  - Added "ReadOnly" configuration option to GanttEditor
  - Fixed GanttTreePanelController log messages
  - Fixed issue with "chain" icon not appearing in GanttEditor
  - Fixed issue with different "icons" per task after loading
  - Fixed issue with icon not changing after setting a task to milestone_p

  Fixed issue with newly created tasks having an empty string
  as an assignees field, instead of an array

- Fixed issue in GanttEditor with loading preferences
  from the wrong user

  (new feature needed from GanttEditor)

  Fixed issue with outer window not being scrolled
  to the top of the screen (and therefore not being
  vixible...)

  which lead to boolean preferences created wrongly.
- Fixed creation of new preferences:
  Added code to store the preference_id returned from the
  REST API into the model. Otherwise it's impossible to
  destroy (DELETE) the preference, if it's not an object...

  - Moved functionality to PO.Utilities.reportError()
  - Eliminated duplicate code from GanttButtonController

  - Created a custom load() function in order to
    load only preferences relevant for the current page.
  - Created a custom sync() function with failure parameter
    in order to handle server errors
  - Created a deferred "bufferedFunction" in order to
    deal with frequent preference updates from scroll events
    and other sources.

- added debug variable to control logging

  Added resize event from "redrawPanel" for initiating a redraw.
  This deals with SplitBorder internal resize between the tree
  and the Gantt drawing area

  and replaced with the URL from the browser.
- Added consistent preference getters for int and
  boolean

  Now using redrawPanel to allow the ResizeController to request a redraw()