Adding support for other databases

[KieranJeffreySmart]

Problem:
I don't want to use postgresql to store the datasets. I assume to have already imported the datasets from csv into my own instance of MS SQL Server and still be compatible with the postcodes.io api by using scripts as described in the posctodes.io documentation

Solution:

• Implement an adaptor pattern into app/models/base.ts to abstract the database operations, using a plugin db_controller to abstract specific database logic and allow new database controllers to be developed and added by the community
• Introduce configuration to app/config/config.ts to support more complex database parameters and select a db controller

I realise this might be incredibly naive as a request, however I am probably going to give it a go myself and would be happy to help find a better solution to my problem