Migrate to flask_sqlalchemy

[samad-yar-khan]

Why do we need this ?

• Our existing approach of using sqlalchemy with flask wanst allowing us to make context bound sessions. It also made difficult for us to handle connection pools.

proposed chnages

• Use Flask_SqlAlchmey
• Updated init for repo
• Update app init
• Update requirements to add Flask_SqlAlchmey
• Update all db models to use db.model and db.column
• Update all repo services to stop roll_back_on_exec usages and use db object for session