Django-zeromigrations

Fixed
- `long_description_content_type` in setup.cfg fixed.

Fixed
- Ignore third-party apps in the process.

Fixed
- Print an error when there is no backup in restoring process.

Added
- `django_migrations` table backup with revision.
- `django_migrations` table restore from last backup.
- Migration files backup from each installed app.
- Migration files restore from backup.
- `zeromigrations` command.