evaluate constrained drag support implications

[cdaniel]

Recent update to jsplumb brings katavorio 0.21.0, which in turn seems to support constrained rectangle where drag and drop may happen. https://github.com/jsplumb/katavorio/commit/b3b3298d9bd9c68382c29f3982e7271e7dfa77f8

This is important, because it opens the editor for:

• pipelines, which can be moved horizontally, but not vertically
• auto-layouts and evolution adjustment only

It needs to be evaluated whethere those use cases could be supported.