Improve path drawing interface

[leomcelroy]

Added better graphical manipulation of path.

• indicate you are editing a path
• preview
• handles for cubics, fillets, chamfers
• automatically display control points when path is selected for points in array format [0, 0]
• delete path or points
• add points to path at specified locations
• convert between point types

[leomcelroy]

All except for adding point at specific index in path addressed with #50