Phase status

In phase model, we have a field status. It is only updated when a new phase is added from the editor. Phase status is determined from start date and end date of a phase in Phase Serializers.

The following should be changed.

TODOs:

• add status and is_final_phase a model property
• remove status and is_final_phase (model filed)
• remove adding status from adding new phase from editor
• remove the logic of getting status from serializers
• add the logic to model
• remove from auto_migrate phase
• test in detail