Implement "new" model in model class

Implement a new keras model in model_class.py. This model has should have the same structure as described in F Kleinert, LH Leufen, and MG Schultz (2020, in preparation).

added Doing enhancement labels

mentioned in commit 1f4e2e9d

added .done label and removed Doing label

mentioned in commit 19bb00e5

added merged in Develop label and removed .done label

closed via merge request !89 (merged)

mentioned in commit e945b365