Add locale; change sources to object with keys = source and value = id

Will update NPM source if PR is accepted & published

- Split models & associations into their own files
- Update columns and requirements
- Create PermissionLevel model & add to relevant models

- Copy Nodemailer and Sequelize fastify plugins to project.
- Upgrade dependencies with yarn upgrade
- Fix break from Sequelize 5 removing Model.find() in AccountController

Add GET /api/shelves/get endpoint;
Turn off test data and pull shelves from database;
Update getLastUpdatedTimestamp to use association function.