Cursor Drifting During Dragging

[zglueck]

This is a follow on to issues #6 and #20 and the solution in commit f67dee9.

@dr3amr2 reported an instance of the UserFacingIcon drifting while being dragged.

Initial review looks like I didn't set the default altitude mode appropriately for the object. Plan is to review other classes and make a slight modification to the drag calculations.

• Check All Defaults
• Modify DraggableSupport to use the CLAMP_TO_GROUND drag position method for objects with 0.0 altitude and RELATIVE_TO_GROUND altitude mode.

[zglueck]

I reviewed all the default altitude modes and dragging methods for objects implementing Draggable and made a few changes. The UserFacingIcon now uses a RELATIVE_TO_GROUND altitude mode which should fix @dr3amr2 issue.

Update is in commit e3e8831