Add group field to StateType and LocalizationType

[marktaipan-cvisionai]

Category
Feature Request

Problem
Current localization and state types cannot be organized into groups (or hierarchy). This can be useful for UI related purposes such as grouping entity types in the annotator context menu.

Request
Add group string type to the StateType and LocalizationType models and expose the new group field in the endpoints / schema. It might be useful to also include a "style" field similar to the one found in AttributeType.