Add node-sass, Pass sass implementation to Grunt config, Add promises…

[SammyMohamed]

I'm following along with the course 'Zero to Production in Node.js' on Pluralsight. I noticed that the readme steps no longer work out of the box, so I'm contributing a few changes that will fix that for other learners.

I've updated the version of grunt-sass as well as the configuration so that there are no longer issues running npm install or running grunt collect_static.

As well, the migrations would not run out of the box. Adding return values and making use of async/await in the migration files appears to fix that issue.