LogScale and LinearScale should inherit from NumericalScale #12
Description
I noticed that LogScale inherits from Scale Python side. But LogScaleModel and LogScale inherits respectively from LinearScaleModel and LinearScale JavaScript side. This means that the LogScale expects some attributes in the widget model that are not set Python side.
I suppose LogScale should at least inherit from LinearScale Python side, and an even cleaner solution could be to have a NumericalScale intermediate class.