Add upsert, save_related, allow dict in fields and exclude_fields, optimisation and cleanup etc.

• Added save status -> you can check if model is saved with ModelInstance.saved property
  • Model is saved after save/update/load/upsert method on model
  • Model is saved after create/get/first/all/get_or_create/update_or_create method
  • Model is saved when passed to bulk_update and bulk_create
  • Model is saved after adding/removing ManyToMany related objects (through model instance auto saved/deleted)
  • Model is not saved after change of any own field (including pk as Model.pk alias)
  • Model is not saved after adding/removing ForeignKey related object (fk column not saved)
  • Model is not saved after instantation with __init__ (w/o QuerySet.create or before calling save)
• Added Model.upsert(**kwargs) that performs save() if pk not set otherwise update(**kwargs)
• Added Model.save_related(follow=False) that iterates all related objects in all relations and checks if they are saved. If not it calls upsert() on each of them.
• Breaking: added raising exceptions if add-ing/remove-ing not saved (pk is None) models to ManyToMany relation
• Allow passing dictionaries and sets to fields and exclude_fields
• Auto translate str and lists to dicts for fields and exclude_fields
• Breaking: passing nested models to fields and exclude_fields is now by related ForeignKey name and not by target model name
• Performance optimizations - in modelproxy, newbasemodel - > less queries, some properties are cached on models
• Cleanup of unused relations code
• Optional performance dependency orjson added (strongly recommended)
• Updated docs