Setup Right access for training.Model

Depends #960 (closed)

Each training model must have dedicated ACL (like corpora & workers for example).

A user or group of user need right access on a Model to view a model and its versions.

• guest users can only view models & their versions with a set tag flag
• contributor users can view models & all their versions and publish new versions without setting the version
• admin can create new versions, edit versions, ...

When a model is public, only its versions with a set tag are available

Please implement a TrainingModelMixin in arkindex/project/mixins.py to cover these methods:

• has_read_access(model)
• has_write_access(model)
• has_admin_access(model)
• readable_models()
• editable_models()