Empty ANNs

[kgd-al]

Currently providing an empty input list (or an empty output list for that matter) does create a "valid" ANN but breaks some assumptions down the line (such as plotly's 3D rendering).
As an empty ANN makes no sense, what should be done:

• Raise an error when creating the ANN (requiring handling code on the client side)
• Gracefully accept it and handle the special cases