Beter relation lines to recognize directions

There is problem to recognize directions for relation lines, eg.

• parent for objects
• constraint properties (note about blue dot lines)

The proposition is to:

• use some gradient for color from start to end (darken from start, lighten to end)
• use bold line on end and thin in begin
• use solid line on end and doted on begin
• add arrows oriented like gizmo (part of this controls)
• multiple of upper options set in preferences