Enable manual database migrations for deployments

[thyb]

The automatic migration may sometimes break. When updating entities, we should generate a migration file that can be applied when deploying the application.

We can use this to generate migrations step: http://docs.sequelizejs.com/manual/tutorial/migrations.html

Migrations should be displayed in Materia designer and should be editable easily.

The migrations could be automatically applied at deployments time to get the same behavior than what we currently have with automatic migration but it would add some control on how the migration is done.

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• Materia Version: v1.0.0-beta.1