Separating layer properties into different sub-classes

[dschick]

Recently, the number of attributes of the layer class has exploded :)
This is because we implemented some very cool new features and simulations.
However, it also makes the interface for the user very overloaded if you actually just need one or two attributes for your simulations.

I already thought a bit about how to separate the parameters, maybe into dictionaries or something alike.
But I think, it would be more pythonic to use inheritance here.

In reality, it would mean that the user has to choose the right type of layer for the simulations.
There could be still the general Layer as the base class.
Then you could decide whether it is amorphous or crystalline and add properties by inheriting e.g. from a MagneticLayer or an AccousticLayer.
Obviously, the naming might be a bit crude, but the concept should work.
However, we need to define most of the relevant layer types in the modules so the user does not have to do it in the script.

Maybe someone has a smarter idea for that?