one when deleting a task

- Now logging an error instead of an alert in case of
  undefined predecessors or successors in dependencies.
  This can happen if the user deletes tasks

  main project as root or not

- Now showing and converting lags according to the lag format
- Extended im_timesheet_task_dependencies by diff_format_id
  and created  categories for representing lag formats
- Fixed saving and loading dependencies in REST
  /intranet-rest-data-source-procs.tcl and
  project-task-tree.json.tcl

- Not yet respecting dependeny "diff"

  doesn't produce bad errors during startup

- Disabled anything except Finish-to-Start dependency in
  the GanttSchedulingController
- Still need to adapt display in GanttBarPanel

  the default status of this feature that can cause performance issues

  when modifying the planned_units
- Added billable_units column
- Added parameter DefaultEnabledColumns in order to allow
  companies define the default columns in the GanttEditor
- Created a new version of GanttEditor in order to enable
  the DefaultEnabledColumns parameter

  by setting the task to the maximum project start
  or end

  - Added code to check for:
    - Dependencies of activities with parents and
    - Cyclic dependencies between activities

  as succ_id and pred_id for dependencies
- Removed old outcommented code
- Included a call to GanttSchedulingController.onRedraw(),
  in order to check for dependencies on parents