Next gen mult-layer

[mtewes]

This issue is just to keep track of an experimental branch.

[mtewes]

Experiments tbd:

• custom multnet optimization function
• use act function on mult-layer
• add a custom "bias" before raising to the power (problem: make this bias individual for each node and input feature -> would be a bias matrix as large as the current weights). But could maybe be implemented without too much effort.