Option to constrain position of blocks to top, middle, and bottom groupings. #39
Description
Through a combination of new YW annotations and properties it should be easy to constrain the positioning of particular process or data blocks to one of three workflow layers corresponding in top-down layout to the top, middle, and bottom of the workflow graph.
Blocks not assigned to a particular layer should be positioned either between the top and middle layer, or between the middle and bottom layers.