Add objectives and tasks from Success Plan Gantt tab

Success plan objectives and tasks can currently only be added on the 'Objectives' tab of the Success Plan. The Gantt tab provides a clearer visual overview of the plan however (and offers more flexibility to move things around), so it would make a CSM's life easier if they could add tasks and new objectives directly from the Gantt tab instead of having to switch between tabs continuously to be able to do this.