Custom Icons and Colors for Milestones

Summary: Enhance the visual representation of milestones in the GANTT plugin by introducing the ability to customize icons and colors. Currently displayed as a generic rhombus, this feature request aims to provide users with the option to select different shapes, potentially using fontawesome.com or a subset of it, and choose colors for a more personalized and informative GANTT view.

1. Icon Selection:
• In the Task window, add a field for typing in or selecting various symbols from a drop-down.
• Empowers users to choose icons that best represent the nature of their milestones.
2. Color Customization:
• Also in the Task window, add a color-picker field to allow users to choose a color for the selected milestone icon.
• Enhances visual clarity and customization, enabling users to differentiate milestones based on color.