Concave Hull b0.7

This node gets points clockwise with a given minimum distance. 

The node has an additional option in the info-palette. Follow Deadlock means, that the hull can follow back the same points that already was used as a hull point. Deadlock off means, that a point can't be uses twice as a hull point.

The Algorithm behind the node:

1. Check, which points are in range of the point most left (bounding box for speed optimization)

2. Check, which points are exactly in range of the distance value

3. Check which angle in cw direction is the smallest and connect to this point

I think there would be a speed optimization possible with normalized vectors etc. So i would call this a beta version of the node.

Computing the angles of the vectors takes a while if there are many points. in combination with the cluster node it takes about 17 seconds for 4200 points. Seven Minutes for 8800 points. So check number of clusters and numbers of points.

The Idea was, to have a workflow for vectorize an image. This is a complexe project. Maybe it is worth to check other algorhitms with existing python external modules. But so far it works quite nice.