Relative modality weights in CubeCreator

[Alvant]

Currently CubeCreator supports only absolute weights (am I right :slightly_smiling_face: ?). Seems that relative weights are more useful (plus taking into account that init_simple_default_model requires relative weights as input). + README should be updated (a part in the end about modality weights): one should emphasize that currently weights should be absolute

Related: #62