Exec connections get drawn to the wrong place

[liamhuber]

As stated, the position for the connection is wonky. I'm 99% sure this is just to do with how I specify the x and y coordinates of the triangle compared to those of the circular data ports. Should be an easy fix, maybe by specifying a new connection_location attribute on these buttons.

Source from Joerg's comment in #54:

• Connecting an exec with a button aligns the node with the edge of the button, not with the center of the circle.