Use database abstraction/ORM layer to support multiple SQL-based database

[joko-sastriawan]

Current MPS database backend is hardcoded to PostgreSQL. As deployments environment varies, connecting to different database means intrusive code editing. In order to ease the adjustment to various deployment condition, database middleware such as knex, sequelize, bookshelf etc should be looked at to provide flexibility.

[rsdmike]

Documentation will be provided and updated here: open-amt-cloud-toolkit/docs#64

[rsdmike]

The linked PR won't solve this, but puts us in the right direction