Composable dragger

[pdavidc]

Create a "dragger" component that can control the "move" behavior of a renderable object, and who's selected implementation can controlled by an application's business logic.

Goal: Allow applications to add their desired dragging behavior to Word Wind components.

Sample Use Cases:

1. Placemarks
2. SurfaceImages
3. Selection handles on a shape editor
4. Placemarks with constrained locations, e.g., satellites in a orbit.