Fix Alpha-helix ribbons

[BradyAJohnston]

Some AH ribbons are a bit mangled, due to the current interpolation of rotations. This should be fixable by doing 'lofting' around the rotation plane of the helix, rather than the current linear interpolation of the rotations.

EDIT:

This issue can track the overall reworking of cartoon internals. With the 'curves to points' node and the new setting custom normal node in 4.1, the internals of these nodes can be greatly simplified.

Will include #236 in this issue to track more potential designs and shapes for the helices.