Added snap dragging to the Gradient gizmo

[jackfruitdog]

Closes #5. This will not apply when a user is dragging the gradient gizmo while holding shift.

[timon-schelling]

This is not complete, the snapping needs to be similar to how snapping with the line tool works, including all overlays that are shown in that case.
The current implementation seems to only snap to the shapes edge not the center point or other useful points or lines.

[jackfruitdog]

This is not complete, the snapping needs to be similar to how snapping with the line tool works, including all overlays that are shown in that case. The current implementation seems to only snap to the shapes edge not the center point or other useful points or lines.

Understood.

[jackfruitdog]

This is not complete, the snapping needs to be similar to how snapping with the line tool works, including all overlays that are shown in that case. The current implementation seems to only snap to the shapes edge not the center point or other useful points or lines.

I added the overlays and more snap points.