Tech Debt: Update Sequelize & Polish + Harden DB Schema

[billdybas]

We're using Sequelize v4, but I think some of the ways we do things are deprecated since v3 or have different syntax. Make sure we're not using outdated conventions and update if we are (http://docs.sequelizejs.com/manual/tutorial/upgrade-to-v4.html). And update our version to the latest v4.

Make sure that on tables we've already created, we have the correct types, default values, null constraints, validations.

Make sure that on relations we've already created, we have the correct on update and on delete actions.

We probably could squash our migrations down, too, since we're still pre-deploy.

[billdybas]

user_shows needs cascade deletes