order of categorical domains

[nandaloo]

Currently, there is no way of setting a default order of values for categorical dimensions. However, this is desirable in a number of scenarios, as often variable values do have a (partially) ordered semantic, even if they are modelled as type categorical.

• [x] check if order in domains.py is propagated to frontend (as this is the real motivation for working on this issue)
  • it is propageted correctly when the models header is requested, however, this information then not used for configuring the order of display...
• [x] figure out how to make it respect the order
• [x] add some way of specifying order. ideas:
  • optional paramter in set_data
  • as explicit function of a dimension
  • as a simple documentation of how to do it (set domain again with differently ordered values)

[nandaloo]

Does https://github.com/lumen-org/modelbase/tree/issue88 fix it? See in particular the jupyter notebook at jupyter/model_training.ipynb that shows an exmple how to do it.