tasks are added _behind_ the currently selected task.
- Fixed Ins/Del keys

  requesting a redraw or enabling the save button

  Now resizing the surface when maximizing the Gantt Editor

  - Rewritten the ZoomController completely.
  - Disabled the ?dc=... value from Ext.Loader in order to allow
    for keeping break points.
  - Now using ganttBarPanel.StartDate instead of StartTime.

  Now showing a message if no tasks are defined yet

  Finally fixed milestone_p issue(?)

  Fixed issue with tasks with exactly equal start_date and end_date

  but at 00:00 and 23:59 respectively
- New tasks now by default take 8 hours to complete

  endDate of tasks are now scheduled at 23:59:59 of the day

- Refactored configuration code
- Created ConfigMenu class in sencha-core

  Fixed issue with end_date < start_date that leads to an error
  from the REST interface originally created by the database
  check-constraint. Now start_date <= end_date is enforced

  - Added CostCenter field
  - Added CostCenter model and store

  - Added read-only functionality and warnings

  (before, the last line was sometimes skipped)

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

  Now produces Beta warning when modifying the tree-model

  Saving the schedule now disables the Save button

- Fixed the display of resources behind a sprite