[Feature] Combined Display of Planned and Real Timeline for Discrepancy Analysis

[rickyweb]

Summary:
Enable a more comprehensive analysis of project timelines in the GANTT plugin by introducing the ability to display both planned and real timelines simultaneously. When either the planned or real dates are provided, the respective timeline is shown. However, when both planned and real dates are available, they should be presented on top of each other for a detailed comparison.

Details:

1. Individual Display:
   • When only planned or real dates are provided: display the respective timeline.
     (currently the timeline is only shown with the data of the planned dates)
2. Simultaneous Display:
   • When both planned and real dates are provided: display the planned and real timelines on top of each other. The planned timeline might be shown as a thin line above the real timeline.