DB: use django-safemigrations for safer deploys

[humitos]

I've found the package https://github.com/aspiredu/django-safemigrate that helps making deployments safer by labeling migrations to be run before deploy, after deploy or always. This is essentially what we do via note cards in our GH release project. However, we need to do this manually at deploy time and it's easy to make mistake here.

I want to propose using this package and get the habit to label the migrations when developing so we make our deploys simpler and easier. Besides, we can adjust our deploy script to be more automated, without the need to jump into web-extra to run these migrations before continuing with the deployment.

[humitos]

We talked a little about this in one of our calls and we said it's a good pattern and idea to implement for safer deploys. We don't have a ETA for this, but it shouldn't be hard to put it under one of the following sprints.